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GIFT  OF 


Main  Lib 


The  Climate  and  Weather  of 
San  Diego,  California 


The  Climate  and 

Weather  of  San  Diego 

California 


PREPARED  UNDER  THE  DIRECTION  OF 

WILLIS  L.  MOORE 

CHIEF  UNITED  STATES  WEATHER  BUREAU 
BY 

FORD  A.  CARPENTER 

LOCAL  FORECASTER 


ILLUSTRATED  WITH   PHOTOGRAPHS  AND  CHARTS   BY  THE 
AUTHOR  AND  OTHERS 


The  term  climate,  in  its  broadest  sense,  implies 
all  the  changes  in  the  atmosphere  which  sensibly 
affect  one's  physical  condition*  — IIUMLOLDT 


PUBLISHED  BY  THE 

SAN  DIEGO  CHAMBER  OF  COMMERCE 


COPYRIGHT,  1913,  BY  THE 
SAN  DIEGO  CHAMBER  OF  COMMERCE 


J.  Horace  McFarland  Company 

Mt.  Pleasant  Press 
Harrisburg,  Pennsylvania 


Captain  Juan  Rodriguez  Cabrillo  entered 
San  Diego  Bay  and  made  the  first  meteoro- 
logical observation  in  what  is  now  San  Diego, 
California,  during  September.  1542* 


281233 


Report;  Clinate  and  Weather 
of  San  Diego. 


STATES  OEPMTHCNT  OF  A6MCUITUM, 

WCATMll    IUIIAU. 
FFICE  OF  THE  CH1IF. 

WASHINOTON.  D.  C.       AUgagt    14,     1912 


Llr.  Ford  A.  Carpenter, 

Local  Forecaster,  Weather  Bureau, 

Iios  Angeles,  Cal. 
Sir: 

Replying  to  your  letter  of  Jane  29,  1912:   I  find 
that  youjreport  on  the  climate  and  weather  of  San  Diego,  Cal., 
has  been  carefully  prepared  In  accordance  with  the  meteorolog- 
ical records,  and  I  therefore  approve  of  Its  publication. 

Such  fruitful  and  conscientious  service  as  you  rendered 
while  official  In  charge  of  the  local  office  of  the  Weather 
Bureau  at  San  Diego  is  helpful  to  the  weather  serrloe  and  is 
appreciated  by  this  Office. 

Very  respectfully, 


Chief  U.S.Weafher  Bureau. 


Table  of  Contents 

CHAPTER  I 

History  of  Weather  Observations  in  San  Diego I 

CHAPTER  II 
The  Velo  Cloud 5 

CHAPTER  III 
Cloud-Forms  in  San  Diego 8 

CHAPTER  IV 

The  Humidity  of  the  Air 12 

CHAPTER  V 
"Desert  Winds"  and  Dust  Storms 16 

CHAPTER  VI 

Fog 19 

CHAPTER  VII 

The  Rainy  Season  in  San  Diego 24 

CHAPTER  VIII 
A  Study  of  Dry  Seasons  in  San  Diego 29 

(vii) 


viii  Table  oj  Contents 

Page 

CHAPTER  IX 
The  Stability  of  the  Climate 33 

CHAPTER  X 
The  Equability  of  the  Climate 41 

CHAPTER  XI 
Climatic  Factors  in  Building 44 

CHAPTER  XII 

The  Coast,  Mountain,  and  Desert  Climates  of  San  Diego 
County 48 

CHAPTER  XIII 
The  Land-and-Sea  Breeze 54 

CHAPTER  XIV 

Aviation  and  Air-Movement  in  San  Diego 57 

CHAPTER  XV 
The  Mirage,  Halo,  and  Aurora 60 

CHAPTER  XVI 
Thunderstorms  and  Other  Rare  Weather  Conditions  —     64 

CHAPTER  XVII 
The  Phenomenon  of  Frost  in  San  Diego 67 


Table  of  Contents  ix 

Page 

CHAPTER  XVIII 

Ocean  Currents  and  Weather  Conditions.  By  Prof.  W.  J. 
Humphreys 69 

CHAPTER  XIX 

Meteorological  Myths 75 

CHAPTER  XX 

Marine  Meteorology  in  San  Diego 80 

CHAPTER  XXI 

Forecasting  San  Diego  Weather 83 

CHAPTER  XXII 

Local  Weather  Signs 88 

CHAPTER  XXIII 
Meteorological  Instruments 92 

CHAPTER  XXIV 
The  Weather  Kiosk  in  the  Plaza 97 

CHAPTER  XXV 
Weather  Exhibits  at  World's  Fairs 102 

CHAPTER  XXVI 
The  Weather  Bureau  and  the  Public 105 

CHAPTER  XXVII 
The  Climate  Summarized  in  Five  Paragraphs 1 1 1 


List  of  Plates 


Facing 

page 

The  Bay  of  San  Diego  from  Point  Loma.  From  a  painting 
by  Fries Frontispiece. . 

Seal  of  San  Diego  Chamber  of  Commerce  (designed  by 
Carpenter)  Vignette v 

The  velo  cloud  over  San  Diego  Bay — U.  S.  S.  Pennsyl- 
vania        6 

Dissipation  of  the  velo  cloud  over  Point  Loma 7 

Cirro-cumulus  cloud  over  Coronado 10 

Cirrus,  alto-stratus,  alto-cumulus  clouds.  Cumulo-nimbus 
in  the  distance  (at  sea) 1 1 

Specimens  of  the  cirro-cumulus  and  alto-cumulus  clouds 
over  the  manufacturing  district  of  San  Diego 18 

Cumulo-nimbus  clouds — Coronado  shore 19 

Cirrus  and  cirro-cumulus  clouds  attending  the  formation 
of  a  well-defined  area  of  low  barometric  pressure 30 

The  Bay  of  San  Diego.    Photographed  above  the  U.  S. 

Naval  Coaling  Station  on  Point  Loma 31 

Hamilton's  flight  over  Point  Lcma 62 

Meteorological  instruments  in  use  at  the  local  office  of  the 
United  States  Weather  Bureau  at  San  Diego 63 

Kiosk  in  San  Diego  Plaza 102 

The    San    Diego    electrical    climatic    exhibit,    Alaska- 
Yukon-Pacific  Exposition,  1909 103 

Strato-cumulus  clouds  over  the  northern  portion  of  San 
Diego  Bay 1 10 

(x) 


List  of  Charts 

(Original  except  chart  on  p.  53) 


Page 

San  Diego  Bay  region  showing  location  of  Weather  Ob- 
serving Stations  since  July,  1849 2 

Chart  showing  moisture  and  winds 14 

Chart  of  annual  temperatures  for  fifty-nine  years 34 

Seasonal  rainfall  chart  for  sixty-two  years 35 

Chart  of  relative  wind  velocity  and  frequency 50 

Comparative  coast,  mountain  and  desert  temperatures, 

and  precipitation 51 

Average  Precipitation  Map  of  California,  being  plate  8 

"Climatology  of  California,"  McAdie 53 

Formation  of  the  land  breeze 55 

Formation  of  the  sea  breeze 55 

Outline  weather  map  of  North  Pacific 71 

Typical  fair  weather  and  rain  maps 85 

Photographic  copy  of  kiosk  thermograph 99 


On) 


List  of  Tables 


Table  No.  Page 

I.  Mean  relative  humidity 13 

II.  Fog  frequency  by  months 21 

III.  Fog  frequency  by  hours 22 

IV.  Average  number  of  rainy  days  by  months 25 

V.  Dry  seasons  in  San  Diego  and  subsequent  sea- 
sonal rainfall 30 

VI.  Normal  rainfall  by  months 31 

VII.  Monthly,  annual,  and  seasonal  rainfall  since  1850 

36,  37 

VIII.  Highest  and  lowest  temperatures,  1874-1912. .  .38,  39 

IX.  Average    highest    and    lowest   temperatures   by 

months 42 

X.  Percentages  of  possible  sunshine  by  months 43 

XI.  San     Diego    County    data     (temperature    and 

weather) 49 

XII.  Average  monthly  and  hourly  wind  movement. .  .     58 

XIII.  Distribution  of  thunderstorms  by  months  and 

hours 64,  65 

XIV.  Comparative  meteorological  data  since  1872. . .    113 
XV.  Meteorological  summary  for  the  year  1911  ...114,  115 


The  Climate  and  Weather  of 
San  Diego,  California 


CHAPTER  I 

HISTORY  OF  WEATHER  OBSERVATIONS 
IN  SAN  DIEGO 

SAN  DIEGO  has  had  an  uninterrupted  govern- 
mental meteorological  record  since  July  i,  1849. 
For  the  first  twenty  years  the  work  was  under 
the  supervision  of  the  Medical  Corps  of  the  Army. 
It  would  be  interesting  to  know  the  name  of  the 
hospital  steward  who  began  the  unbroken  record  of 
San  Diego's  temperature  and  rainfall  observations 
on  that  distant  July  day.  The  thermometers  and 
rain-gage  were  placed  in  the  shadow  of  the  walls  of 
the  old  San  Diego  mission,  which  were  standing, 
though  even  then  in  a  dilapidated  condition.  The 
United  States  troops  used  the  old  mission  as  head- 
quarters for  a  year;  afterwards  the  military  post 
was  transferred  to  the  vicinity  of  the  old  Mexican 
presidio  at  what  is  now  Old  Town.  It  speaks  well 
for  the  discipline  of  the  Medical  Corps  of  the  Army 
that  meteorological  observations  (which,  in  the  early 
days,  were  part  of  the  post  surgeon's  duties)  were 
continued,  without  a  break,  until  the  instruments  and 
records  were  transferred  to  the  Signal  Service  on 
November  i,  1871.  Between  1856  and  this  transfer 
the  location  of  the  instruments  was  changed  twice — 

(i) 


2        Climate  and  Weather  oj  San  Diego 

both  times  nearer  the  present  site  of  San  Diego. 
During  the  past  half-century  the  meteorological 
instruments  have  been  located  within  a  radius  of 
half  a  mile.  The  weather  observations  in  new  San 
Diego  were  first  made  at  the  old  H  Street  barracks; 
fifteen  years  later,  when  the  Signal  Service  assumed 
control,  the  office  was  established  in  Horton  Square, 
later  changing  to  the  site  of  the  present  Union 
Building;  then  to  the  corner  of  Fifth  and  D  Streets, 
and  again  to  Fifth  and  F  Streets,  where  the  weather 
office  is  at  present  located.  When  the  new  Federal 
Building  is  finished  in  the  early  part  of  the  year  1913, 
the  Weather  Bureau  will  have  completed  its  half- 
mile  circle  of  wanderings  back  to  its  starting-place 
at  the  old  military  reservation. 

The  following  sketch-map  of  the  San  Diego  Bay 
region  indicates  the  various  locations  of  the  meteoro- 
logical station  from  1849  to  date. 


San  Diego  Bay  Region,  showing  location  of  the  United  States 
Weather-Observing  Stations  since  July,  1849 


Weather  Observations  in  San  Diego         3 

NON-INSTRUMENTAL  WEATHER  OBSERVATIONS 
BEGAN   IN    1542 

The  non-instrumental  observations  of  San  Diego 
weather  occur  in  the  writings  of  many  famous  men 
during  the  past  370  years:  Cabrillo,  in  1542;  Vis- 
caino,  in  1602;  Serra,  in  1769;  Dana,  in  1835; 
Agassiz,  in  1872;  and  Greely,  in  1888,  have  con- 
tributed to  its  meteorology.  The  first  record  we 
have  is  from  Juan  Rodriguez  Cabrillo,  the  dis- 
coverer of  San  Diego  Bay,  who  entered  in  his  ship's 
log  in  September,  1542: 

A  very  great  gale  blew  from  the  southwest;  the  port 
being  good,  we  felt  nothing. 

Sixty  years  later  Sebastian  Viscaino  surveyed  the 
harbor,  and  made  the  first  observations  of  any  con- 
siderable value.  Father  Junipero  Serra,  in  July, 
1769,  established  at  San  Diego  the  first  mission  in 
California.  In  his  letters  home  he  mentioned  the 
similarity  of  this  climate  to  that  of  his  beloved  Spain. 
Sixty  years  later  Richard  Henry  Dana  visited  San 
Diego,  and,  in  his  "Two  Years  Before  the  Mast," 
gave  an  account  of  the  early  days  in  this  region  that 
will  forever  remain  a  classic.  In  commenting  on 
the  storm-winds  of  California,  Dana,  in  1835,  said: 

This  wind  [the  southeaster]  is  the  bane  of  the  coast  of 
California.  Between  the  months  of  November  and  April, 
including  a  part  of  each  (which  is  the  rainy  season  in 
this  latitude),  you  are  never  safe  from  it;  and  accordingly, 
in  the  ports  which  are  open  to  it,  vessels  are  obliged  during 
these  months  to  lie  at  anchor  at  a  distance  of  three  miles 
from  the  shore,  with  slip-ropes  on  their  cables,  ready  to 
slip  and  go  to  sea  at  a  moment's  warning.  The  only 


4         Climate  and  Weather  of  San  Diego 

ports  that  are  safe  from  this  wind  are  San  Francisco  and 
Monterey  in  the  north  and  San  Diego  in  the  south. 

Some  are  still  living  in  San  Diego  today  who 
heard  Alexander  Agassiz,  in  1872,  give  his  impres- 
sions of  his  visits  to  San  Diego  in  the  following 
words: 

In  enumerating  the  peculiar  advantages  of  San  Diego, 
there  seems  to  be  one  which  is  of  very  great  importance. 
Perhaps,  as  a  scientific  man,  /  may  lay  more  stress  upon 
it  than  is  necessary,  but  I  hardly  think  it  possible;  I  have 
seen  many  parts  of  the  world,  and  have  made  some  study 
of  this  subject.  It  is  the  question  of  the  climate  of  your 
latitude  that  I  refer  to.  You  have  a  great  capital  in  your 
climate.  It  will  be  worth  millions  to  you.  This  is  one 
of  the  favored  spots  of  the  earth,  and  people  will  come  to 
you  from  all  quarters  to  live  in  your  genial  and  healthful 
climate,  a  climate  that  has  no  equal. 

To  bring  this  chronological  history  up  to  the 
close  of  the  nineteenth  century,  the  following  quota- 
tion is  made  from  a  former  resident,  General  A. 
W.  Greely.  When,  as  Chief  Signal  Officer  of  the 
Army,  he  was  at  the  head  of  the  United  States 
Weather  Service,  he  contributed  a  paper  on  the 
climates  of  the  United  States.  In  this  article  he  said: 

The  American  public  is  familiar  on  all  sides  with 
elaborate  and  detailed  statements  of  the  weather  at  a 
thousand  and  one  resorts.  If  we  may  believe  all  we  read 
in  such  reports,  the  temperature  never  reaches  the  eighties, 
the  sky  is  flecked  with  just  enough  of  cloud  to  perfect 
the  landscape,  the  breezes  are  always  balmy,  and  the 
nights  ever  cool.  There  is  possibly  one  place  in  the 
United  States  where  such  conditions  obtain — a  bit  of 
country  about  forty  miles  square,  at  the  extreme  south' 
western  part  of  the  United  States,  in  which  San  Diego, 
California,  is  located. 


CHAPTER  II 
THE  VELO  CLOUD 

THE  challenge,  "We  all  know  the  winters 
are  warm  in  San  Diego,  therefore  the  sum- 
mers must  be  hot,"  constitutes  the  most  com- 
mon misunderstanding  of  San  Diego's  cool  summers. 
The  fact  that  there  is  less  than  one  hour  per  year 
above  90  degrees  is  not  easy  to  explain,  until  we 
remember  the  old  Mexican  phrase,  El  velo  de  la  luz, 
"The  veil  that  hides  the  light."  This  is  a  folk-lore 
expression,  originating  not  only  before  the  Gringo 
came,  but,  doubtless,  long  before  the  coming  of 
the  old  Spanish  conquistadors.  The  better-known 
English  term,  "high  fog,"  has,  in  common  with  most 
words  of  pur  language,  a  double  meaning,  and  it 
is  misleading  to  a  non-resident.  It  is  not  fog  in 
the  generally  accepted  meaning,  for  this  "light- 
veil"  is  neither  cold  nor  excessively  moisture-laden. 
Neither  is  it  high,  for  its  altitude  is  less  than  a 
thousand  feet. 

To  one  who  has  spent  a  few  weeks  of  spring, 
summer,  or  fall  in  southern  California,  the  pictur- 
esque description  of  the  musical  Spanish  el  velo  is 
quickly  recognized  as  both  expressive  and  truthful. 
A  noted  English  traveler  gave  his  views  on  the 
"t?e/o"  cloud  in  a  communication  to  the  San  Diego 
"Union."  He  said: 

/  am  glad  that  the  old  Spanish  word  "velo"  is  brought 
to  light.  The  velo  cloud  is  so  expressive  of  the  lovely 
diaphanous  cloud  that,  of  a  midsummer's  morning,  shades 

(5) 


6        Climate  and  Weather  of  San  Diego 

San  Diego's  brilliant  sun  until  such  time  as  the  "veil" 
is  swept  aside  by  the  ocean  breeze,  whose  cooling  breath 
renders  it  no  longer  necessary  for  a  perfect  day  by  the 
"Harbor  of  the  Sun"  I  have  always  felt  sure  that  those 
fine  old  Spaniards  never  damned  so  good  a  thing  by  such 
an  abusive  and  misleading  term  as  "high  fog."  As  bearing 
on  the  new,  yet  very  old,  word  "velo"  I  remember  that  one 
day  in  April,  when  off  the  coast  of  Lower  California,  an 
intelligent  Spanish  gentleman  referred  to  this  very  cloud 
condition  as  the  "velo  qui  cubre  la  luz  del  sol."  I  also 
beard  it  spoken  of  as  "el  velo  de  la  manana,"  showing  that, 
while  many  phrases  are  used,  the  leading  idea  is  the 
poetic  one  of  a  "veil." 

THE  VELO  IS  A  CHARACTERISTIC  CLOUD 

While  the  velo  cloud  is  common  to  the  Pacific 
coast  generally,  and  has  been  observed  as  far  north 
as  the  Straits  of  Fuca,  this  cloud  reaches  its  per- 
fection over  the  littoral  region  of  southern  Cali- 
fornia. The  velo  cloud  is  the  chief  characteristic 
of  the  summer  climate  of  the  San  Diego  Bay  region. 
And  summer  should  be  understood  as  covering  all 
the  year  excepting  November,  December,  January, 
and  February.  These  four  months  could  easily  be 
reckoned  as  spring-time.  The  screening  of  this 
region  from  the  sun's  rays  is  so  thoroughly  accom- 

Elished  that,  during  a  normal  summer's  day,  the  sun 
reaks  through  the  velo  cloud  about  10  o'clock,  the 
sky  clearing  shortly  afterwards  and  remaining  free 
from  clouds  until  about  sunset.  That  the  velo 
cloud  is  effective  as  a  sun-shield,  it  needs  only  to  be 
stated  that  the  average  of  all  the  July  maximum 
temperatures  since  weather  observations  began 
shows  a  mean  of  about  78  degrees. 


The  Velo  Cloud  7 

The  cause  of  the  formation  of  the  velo  cloud  and, 
consequently,  the  cool  summers  of  San  Diego,  is, 
strange  to  say,  found  in  the  hot  weather  in  the 
interior  of  California  and  Arizona.  It  is  a  unique 
example  of  the  aptness  of  the  proverb,  "It's  an  ill 
wind  that  blows  nobody  good."  The  hot  weather 
in  the  interior  produces  an  aerial  eddy  (the  "low"  of 
the  weather  map),  and  the  difference  in  atmos- 
pheric pressure  between  the  interior  and  the  ocean 
results  in  giving  San  Diego  cool,  uniform  days  and 
nights,  free  from  extremes,  or  what  is  really  the 
summer  temperature  of  the  Pacific  Ocean.  The  velo 
cloud  should  therefore  be  incorporated  in  our  local 
vocabulary,  and  it  should  replace  the  misnomer, 
"high  fog." 


CHAPTER  III 
CLOUD-FORMS  IN  SAN  DIEGO 

CHIEF  among  the  characteristics  of  the  weather- 
in  San  Diego  from  November  until  March  is 
the  great  variety  and  beauty  of  cloud-forms. 
It  is  unusual  that,  in  a  locality  of  such  marked 
equability  in  temperature,  abundant  sunshine,  and 
light  rainfall,  there  should  be  such  a  variety  in  the 
formation  of  the  clouds.  The  records  of  the  Weather 
Bureau  since  their  beginning  in  this  locality,  forty 
years  ago,  devote  much  space  to  this  interesting  and 
important  meteorological  feature.  An  examination 
of  these  records,  and  the  taking  of  hundreds  of  cloud- 
photographs,  together  with  personal  observations 
extending  through  a  period  of  over  a  dozen  years, 
incline  one  to  the  belief  that  there  is  practically  no 
variety  of  clouds  which  has  not  at  some  time  been 
seen  in  San  Diego.  A  discussion  of  local  cloud- 
forms  would,  therefore,  include  nearly  all  of  the 
known  varieties  and  many  that  are  uncommon  to 
other  lands. 

The  cause  of  cloudiness  is  the  condensation  of 
the  water-vapor  in  the  atmosphere.  The  com- 
position of  clouds  includes  all  the  various  forms  of 
suspended  moisture,  ranging  from  the  water  parti- 
cles of  the  rain-cloud  to  the  minute  ice  spiculae  of 
the  high  cirrus  cloud.  The  type  of  cloud  most 
likely  to  be  formed  depends  on  elevation,  relation- 
ship to  the  great  atmospheric  centers  of  low  and 
high  pressure,  and  the  physical  configuration  of  the 
land. 

(8) 


Cloud-Forms  in  San  Diego  9 

EXPLANATION  OF  THE  CLOUD-CREST  ON  POINT  LOMA 

A  beautiful  example  of  local  condensation  may 
be  seen  when  the  narrow  promontory  of  Point  Loma 
is  covered  with  fog,  while  the  rest  of  the  atmosphere 
is  clear.  As  the  vapor  is  blown  against  the  sides  of 
this  promontory,  it  is  forced  upwards  a  few  hundred 
feet,  and,  according  to  the  law  that  the  temperature 
is  lowered  one  degree  for  every  300  feet  of  ascent, 
the  air  is  immediately  cooled  by  expansion,  the  tem- 
perature of  saturation  is  reached,  and  the  crest  of 
Point  Loma  is  covered  with  a  beautiful  mantle  of 
glistening  fog,  rivaling  the  historic  "table-cloth"  on 
Table  Mountain  in  Cape  Town,  South  Africa.  As 
both  the  white  mantle  over  Point  Loma  and  the 
table-cloth  on  Table  Mountain  are  produced  by 
the  same  conditions,  a  rise  in  temperature  of  so 
much  as  a  few  degrees  will  dissipate  these  interest- 
ing spectacles.  These  illustrations  show  that  moist- 
ure is  mixed  with  the  air,  visible  as  fog,  but  always 
present  whether  visible  or  not. 

EVERY    CLOUD    HAS    ITS    OWN    INDIVIDUALITY 

There  are  four  distinct  varieties  of  clouds — 
stratus,  cumulus,  nimbus  and  cirrus,  and  these  are 
further  separated  into  a  total  of  ten  classes.  The 
study  of  the  clouds  in  southern  California  is  so 
interesting  that  it  will  well  repay  a  brief  considera- 
tion of  their  formation  and  significance.  Beginning 
with  the  cloud  nearest  the  earth  we  have  the  stratus, 
which  is  a  uniform  layer  of  cloud  with  an  altitude 
of  less  than  a  thousand  feet.  In  summer  it  is  the 
velo  cloud  of  southern  California.  The  nimbus 


io       Climate  and  Weather  of  San  Diego 

cloud  is  the  rain-producer,  and  it  is  frequently 
accompanied  by  brisk  southerly  winds.  The  cumulo- 
nimbus is  the  thunder-head  of  the  spring  and  sum- 
mer. These  clouds  are  often  seen  towering  over  the 
Cuyamaca  and  Palomar  Mountains,  thrusting  their 
snow-white  masses  several  miles  up  into  the  air. 
They  are  always  associated  with  the  "Sonora" 
storms  of  spring.  This  form  is  the  most  transient 
of  clouds,  lasting  in  this  region  less  than  an  hour. 
The  cumulus  is  the  fair-weather  cloud,  and  is  due  to 
ascending  currents  of  moisture-laden  air.  The 
strato-cumulus  is  distinguished  by  wave-like  rolls  of 
dark  cloud  through  which  the  sun  sends  shafts  of 
light,  producing  the  spectacle  of  "the  sun  drawing 
water."  The  alto-stratus  is  a  thick  veil  through 
which  the  sun  may  be  faintly  seen,  and,  as  the  sailors 
say,  "making  the  stars  look  sick."  In  San  Diego 
it  is  nearly  always  a  threatening  sky,  as  rain  fre- 
quently follows  its  appearance.  The  alto-cumulus 
is  another  threatening  cloud,  but  only  when  its 
fleecy  masses  show  pendent  hemispherical  shapes. 
This  is  the  cloud  which  supplies  the  brilliant  red 
sunsets.  The  cirro-cumulus  cloud  is  composed  of 
small  fleecy  balls,  and  is  sometimes  seen  in  company 
with  irregular  streamers  of  cirrus  cloud.  These 
clouds  are  among  the  most  beautiful  to  be  seen  in 
this  locality.  They  assume  parallel  bands,  which 
seem  to  converge  and  appear  to  give  truth  to  Omar 
Khayyam,  when  he  sang  of  the  sky  as  "that  inverted 
bowl  they  call  the  sky."  In  observing  cloud-forma- 
tions it  should  be  borne  in  mind  that  perspective 
is  responsible  for  the  many  illusions  presented  to 
the  eye.  The  cirro-stratus  is  a  still  higher  cloud,  and 
its  veil-like  consistency  gives  a  foreboding  aspect  to 


u 


Cloud-Forms  in  San  Diego  n 

the  sky.  This  cloud  produces  the  lunar  and  solar 
halos,  "sun  dogs,"  and  kindred  optical  phenonema. 
The  cirrus  cloud  is  the  highest  cloud  of  any  perma- 
nence in  the  category,  having  an  altitude  of  from 
10,000  to  30,000  feet,  and,  owing  to  this  great  height, 
it  is  composed  of  spiculae  of  ice.  This  feathery  cloud 
is  of  infrequent  occurrence  over  southern  California, 
as  it  is  always  associated  with  storm-areas.  The 
appearance,  direction,  and  duration  of  the  cirrus 
wisps  often  constitute  the  best  indication  to  the 
sailor  of  the  location  of  storm-centers.  Among  the 
rare  clouds  seen  in  San  Diego  are  "whirling  cumulus," 
the  spiral  clouds  of  the  upper  atmosphere;  the  "fes- 
tooned nimbus,"  from  which  the  waterspout  has 
its  birth;  and  the  evanescent  "cloud  banner,"  which 
streams  out  from  Cuyamaca  Peak. 


CHAPTER  IV 

THE  HUMIDITY  OF  THE  AIR 

THERE  is  considerable  truth  in  the  oft-repeated 
statement  that  "San  Diego  has  the  driest 
marine  climate,"  provided,  of  course,  that 
the  comparison  is  made  with  other  seaports  of  the 
United  States.  The  phrase  needs  some  explanation, 
for  a  "dry  marine  climate"  might  be  more  moist  than 
a  damp  continental  climate.  Water  is  always  present 
in  the  atmosphere,  whether  the  air  is  so  dry  as  to 
be  uncomfortable,  or  so  moist  that  fog  obscures 
the  vision.  This  vapor  of  water  exists  in  addition 
to  the  air,  and  should  be  considered  as  a  different 
element.  The  usual  method  of  measuring  the 
amount  of  moisture  in  the  air  is  in  percentages  of 
saturation  with  relation  to  the  temperature,  hence 
the  term  relative  humidity.  In  San  Diego  the  rela- 
tive humidity  varies  throughout  the  year,  being 
greatest  in  the  spring  and  summer  months  and  least 
m  the  fall  and  winter.  The  average  annual  relative 
humidity  is  75  per  cent.  The  record  shows  that 
during  the  so-called  "desert-winds"  observations 
of  but  2  or  3  per  cent  of  relative  humidity  are  not 
uncommon.  This  drying  air  is  irritating  to  the 
nerves,  owing  to  its  effect  on  the  tissues  and  mem- 
branes; but  the  good  effect  of  this  radical  change  in 
atmospheric  surroundings  cannot  be  overlooked. 
The  thorough  drying  out  and  cleansing  that  is 
given  the  coast  region  makes  mildew  and  mold, 
while  common  to  most  seacoast  regions,  unknown 
to  the  region  about  San  Diego.  Observations  of  the 

(12) 


The  Humidity  oj  the  Air  13 

physiological  effect  of  damp  air  and  dry  air  show 
that  dampness  depresses  the  nerves,  induces  sleep 
and  slower  circulation  of  blood,  while  dry  air  causes 
more  or  less  nervous  excitement,  sleeplessness, 
quickens  the  pulses,  dries  the  skin,  and  tends  toward 
decreased  bodily  temperature. 

The  automatic  registration  of  humidity  also 
shows  that  the  greatest  relative  humidity  occurs 
shortly  after  midnight,  and  the  least  about  noon. 
There  is  thus  seen  to  be  a  close  relationship  between 
air-moisture  and  air-temperature,  for  the^  vapor- 
capacity  increases  proportionately  with  increase 
in  temperature.  When  the  relative  humidity  is  low, 
the  atmosphere  is  drying,  or  has  a  tendency  to  raise 
more  vapor  from  water  or  damp  soil.  When,  on  the 
other  hand,  the  relative  humidity  is  high,  there  is 
little  tendency  to  evaporation,  and  a  slight  fall  in 
temperature  leads  to  saturation  and  condensation, 

TABLE  I. — Mean  Relative  Humidity,  Twenty-Jour  Years, 

l888    tO    IQll 

January 71  July 80 

February 74  August 80 

March 74  September 78 

April 75  October 76 

May 77  November 71 

June 79  December 67 

Annual 75 

The  chart  (p.  14)  gives  the  direction  and  humidity 
of  the  different  winds  that  blow  in  San  Diego,  the 
length  of  the  heavy  line  indicating  the  relative 
humidity  of  the  wind,  from  each  given  direction. 

It  will  be  seen  that  the  wind  from  the  northeast 
is  the  driest,  and  the  wind  from  the  northwest  the 
most  humid;  the  latter  carrying  over  four  times  as 
much  moisture  as  the  former.  Relative  humidity 


14       Climate  and  Weather  of  San  Diego 

depends  not  only  upon  the  amount  of  moisture  in  the 
atmosphere  in  any  given  locality,  but  also,  and 
largely,  upon  the  actual  exposure.  For  instance, 
while  the  relative  humidity  of  the  location  may  be  as 
high  as  80  per  cent,  the  relative  humidity  in  a  room 
facing  south  or  east,  with  open  windows,  may, 
because  of  its  higher  temperature,  be  as  low  as  50 
per  cent.  Local  environment  plays  a  most  important 


Wind 
Direc- 
tion 

Relative  Humidity  in  Per  Cent. 

10    20  30   40   50  60   70  80  90    100,. 

per- 
cent 

A/. 

£ 

S.E. 

s 

p^^^^J  '  1  '  1  ;  |  '  1  '  1  '  1  '  1 

60 
20 
25 
40 
55 

sw 

60 

w 

75 

N.W. 

85 

Chart  showing  moisture  and  winds 

part  in  the  physical  effects  of  moisture.  The  climate 
of  San  Diego  City  is  a  cool,  moist  climate  with  much 
sunshine.  If  a  drier  atmosphere  is  required  for 
residence,  it  would  be  necessary  to  go  eastward  into 
the  desert  region,  where  there  is  a  dry,  warm,  and 
windy  climate. 

Humidity  is  a  friend — not  a  foe,  provided  that 
the  accompanying  temperature  is  moderate.  It  is 
only  when  the  air  is  hot  and  humid  that  the  weather 
is  sultry.  "Raw  winds"  are  possible  only  when  the 


The  Humidity  oj  the  Air  15 

temperature  is  low  and  the  humidity  is  high.  Balmy 
weather,  so  much  sought  for,  may  be  considered  as 
having  temperatures  varying  from  65  to  75  degrees, 
with  accompanying  relative  humidities  of  from  70 
to  90  per  cent. 

There  is  no  doubt  but  that  the  phrase  "relative 
humidity"  has  been  given  too  prominent  a  place  in 
discussing  the  climatic  advantages  and  disadvan- 
tages of  a  region.  It  is  simply  a  ratio  varying  with 
temperature.  As  has  been  well  said,  "The  absolute 
weight  of  the  water- vapor,  the  relative  purity  of  the 
air,  and  the  frequency  of  ventilation  are  the  things 
that  count  in  the  health-giving  character  of  a 
climate." 


CHAPTER  V 
"DESERT  WINDS"  AND  DUST  STORMS 

ONE  of  the  paradoxes  of  the  climate  of  San 
Diego  is  its  almost  entire  freedom  from 
dust  storms.  Ordinarily  the  combination  of 
sea  breeze,  abundant  sunshine,  and  a  location  in  a 
region  having  the  desert  conditions  of  less  than  ten 
inches  of  rain  annually,  would  seem  to  make  it  an 
ideal  region  for  frequent  dusty  winds.  Dust  storms 
require  two  elements,  which  are  absent  in  this 
locality:  First,  finely  divided  soil  and,  second, 
brisk,  drying  winds.  These  conditions  are  often 
met  with  over  the  plains  states — the  states  in  the 
inter-mountain  region  and  in  the  southwestern 
plateau  region.  In  such  localities  the  wind  and 
dust  are  among  the  most  disagreeable  features. 
The  highest  wind  occurs  during  the  middle  of  the 
day,  and  carries  with  it  the  soil,  which  is  com- 
monly of  a  chalk-like  consistency.  This  dust  sifts 
through  close-fitting  doors  and  windows  of  resi- 
dences and  offices,  its  flour-like  nature  enabling  it  to 
enter  nearly  everywhere.  Such  is  the  condition 
generally  described  by  residents  of  many  western 
states. 

WHY  SAN  DIEGO  IS  IMMUNE  FROM  DUST  STORMS 

San  Diego  is  practically  immune  from  dust 
storms  because  the  soil  is  too  coarse  and  the  winds 
are  not  high.  The  soil  in  this  region,  being  mostly 
of  decomposed  granite,  is  not  light  in  weight,  nor 

(16) 


"Desert  Winds"  and  Dust  Storms        17 

does  it  occur  in  a  pulverized  state.  While  the  winds 
are  steady,  they  are  not  often  brisk  or  drying.  Of 
course,  as  one  approaches  the  higher,  drier,  and 
more  exposed  localities,  the  winds  are  stronger  and 
the  air  has  less  moisture.  The  local  Weather  Bureau 
Station  has  no  record  of  storms  of  dust  damaging 
either  residents  or  vegetation,  although  a  generation 
has  passed  since  the  establishment  of  the  Station. 
The  barometric  pressure  in  southern  California  is 
remarkably  even  and  free  from  extremes.  New 
residents  sometimes  express  themselves  disgusted 
with  the  sluggish  condition  of  their  much-prized 
aneroid  barometer,  which,  in  their  eastern  homes, 
showed  generous  variation  in  pressure.  In  San 
Diego  the  barometer  indicates  little  change  from 
day  to  day;  it  averages  a  trifle  below  thirty  inches, 
and  it  has  a  daily  range  of  about  one-tenth  of  an 
inch.  This  removes  another  factor  in  dust  distribu- 
tion, for  it  is  a  well-known  fact  that  rapidly  varying 
atmospheric  pressure  alternately  pumps  the  air 
from  "dust-proof"  cabinets  and  cupboards,  or  drives 
in  the  dust-laden  air. 

The  mechanics  of  the  high,  dry  wind  are  among 
the  most  interesting  features  in  meteorology.  In 
the  region  of  the  plains  states,  the  immense  areas 
of  high  barometric  pressure  pour  down  masses  of 
dry  air,  which  becomes  hot  in  summer,  and  is  cold  in 
winter.  This  high-pressure  wind  laps  up  moisture. 
In  southern  California  the  only  high  barometric  pres- 
sure areas  which  can  affect  the  local  climate  form 
either  off  the  Washington  or  Oregon  coast,  or  off  the 
California  coast;  in  both  instances  they  generally 
move  directly  eastward.  Once  in  a  while  these 
areas  trend  southeasterly,  and  they  remain  stagnant 


1 8       Climate  and  Weather  of  San  Diego 

long  enough  to  set  up  air-circulation  sufficient  to 
affect  the  weather  in  San  Diego.  Then  there  occur 
what  are  locally  termed  "desert  winds." 

DESERT  WINDS 

If  a  stranger  should  ask  a  resident  of  southern 
California  what  month  of  the  year  is  the  warmest, 
he  would  very  likely  name  November.  And,  if  he 
should  question  further,  he  would  probably  be 
informed  that  it  was  the  warmest  because  of  the 
prevalence  of  the  "desert  winds,"  which  are  more 
common  during  November  than  in  any  other  month 
of  the  year.  The  desert  wind  does  not  originate  in 
the  desert,  even  though  the  air-movement  at  such 
times  is  from  nearly  the  direction  of  the  desert.  It 
partakes  of  that  nature  both  in  temperature  and 
dryness.  Its  name  differs  with  its  habitat, — it  is 
variously  called  a  "norther"  a  "Santa  Ana,"  or  by 
the  name  of  some  other  town  north  of  the  one 
experiencing  such  weather. 

There  are  some  desirable  features  in  the  desert 
wind, — it  certainly  does  more  good  than  harm  to 
San  Diego.  It  is  as  if  the  whole  of  the  San  Diego 
Bay  region  were  transported  to  the  mountains  and 
the  desert,  and  allowed  to  remain  in  that  clear, 
bracing,  and  germ-destroying  air  for  periods  of 
two  or  three  days. 


Specimens  of  the  cirro-cumulus  and  alto-cumulus  clouds 
over  the  manufacturing  district  of  San   Diego 


CHAPTER  VI 
FOG 

BETWEEN  the  same  parallels  of  latitude  in 
the  United  States,  the  Pacific  Coast  experi- 
ences more  frequent  fog  than  the  Atlantic 
Coast.  The  reason  for  this  is  that  with  the  general 
drift  of  the  air  with  the  revolution  of  the  earth, 
the  winds  of  the  Pacific  Coast  are  mostly  on- 
shore, while  those  of  the  Atlantic  are  off-shore.  The 
distribution  of  fog  on  the  Pacific  Coast  reaches 
its  maximum  at  San  Francisco,  with  moderately 
high  averages  north  to  the  Canadian  boundary, 
and  decreasing  in  frequency  and  duration  with 
the  latitude,  San  Diego  having  the  least  on  the 
coast. 

Fog-charts,  prepared  by  the  Marine  Division  of 
the  Weather  Bureau,  show  that  there  have  been 
fogs  on  the  Pacific  Coast  which  covered  the  shore- 
line from  Canada  to  Mexico  with  a  blanket  of  fog 
averaging  fifty  miles  in  width.  So  far  as  San  Diego 
is  concerned,  the  greatest  fog-bank  of  which  there 
is  any  record  occurred  a  few  years  ago,  when  the 
fog  extended  200  miles  westward.  Even  when  the 
fog  is  most  dense  it  has  only  a  slight  vertical  thick- 
ness. This  fact  was  well  borne  out  by  the  experiences 
of  the  naval  officers  in  the  fleet  maneuvers  off  San 
Diego,  in  1910,  which  were  interrupted  for  a  day  or 
two  only  by  fog.  On  one  occasion  the  position  of  the 
ships  of  one  of  the  squadrons  could  be  discerned  only 
from  the  military  tops  by  noting  the  tips  of  the 
masts  which  showed  above  the  fog. 

(19) 


20       Climate  and  Weather  oj  San  Diego 

FOG  AND   RAIN   DIFFER  ONLY   IN   EXTENT  OF 
CONDENSATION 

While  fog,  cloud,  and  rain  are  but  differing 
degrees  of  condensation,  there  is  not  the  relationship 
between  fog  and  cloud  that  exists  between  cloud 
and  rain.  Concisely  stated,  the  difference  between 
rain  and  fog  is  that  while  rain  is  caused  by  expansion 
and  consequent  cooling  of  the  air,  fog  is  caused  by 
the  cooling  of  the  air,  either  by  radiation  or  by  con- 
duction. In  the  first  process  the  water-vapor 
becomes  visible  as  cloud  whenever  the  air  has 
carried  the  vapor  upward  till  it  has  cooled  by  expan- 
sion to  a  temperature  below  the  dew-point;  in  the 
other,  the  water-vapor  becomes  visible  as  a  result, 
usually,  of  intermingling  with  air  that  had  been 
cooled  by  the  surface  of  the  earth,  which  itself  had 
lost  heat  by  radiation.  Fog  always  ends  one  of  the 
three-day  warm  periods  such  as  San  Diego  infre- 
quently experiences.  The  explanation  is  as  follows: 
The  high  barometric  pressure,  which  primarily 
causes  the  high  temperature  during  such  periods, 
moves  eastward  and  loses  its  effect  over  the  Pacific 
slope.  The  consequent  indraft  from  the  sea  brings 
quantities  of  warm  and  moist  air  over  the  cooler 
waters  of  the  shore  and  bay.  The  irregularity  of  the 
fog-wreaths  and  -billows,  and  the  erratic  distribution 
of  fog  over  the  bay,  may  be  assigned  to  the  differing 
depths  of  water,  for  the  deeper  the  water  the  cooler 
it  is,  and,  therefore,  the  lower  the  temperature  of 
the  air  immediately  above  it.  These  fog-banks  and 
-billows  make  aerial  signals,  such  as  whistles  and 
bells,  uncertain  and  deceptive.  Unless  the  fog  is  of 
uniform  thickness,  and  is  without  intervening 


Fog  21 

pockets  of  fog-free  air,  submarine  sound-signals  are 
the  only  reliable  warnings.  The  echo  from  the 
steamer's  whistle  will  be  returned  by  a  vertical  bank 
of  dense,  cold  air  as  perfectly  as  if  the  sound  had  been 
reflected  by  the  shore.  Sometimes  fog-billows  may 
be  seen  almost  to  touch  the  water  yet  extend  upward 
in  rounded  masses.  Some  of  the  most  beautiful 
effects  of  sunlight  on  fog-masses  are  observed  under 
such  combinations  of  temperature  and  moisture. 
Daylight  fogs  are  practically  unknown  in  San  Diego, 

AVERAGE  FREQUENCY  OF  FOG   IN  DIFFERENT 
MONTHS 

In  view  of  the  rapidly  increased  shipping  in  and 
out  of  San  Diego  harbor,  the  following  table  will  be 
found  interesting  and  of  value: 

TABLE  II. — Number  oj  Days  with  Fog 

January 2  July I 

February 2  August I 

March i  September 2 

April 2  October 5 

May i  November 3 

June i  December i 

A  "day  with  fog"  is  one  on  which  there  is  one 
hour  or  more  of  fog  dense  enough  to  obscure  objects 
a  thousand  feet  distant.  The  data  are  from  the 
records  of  fifteen  years'  duration.  During  the  year 
1911  a  detailed  study  of  fog  conditions  was  made, 
covering  density  and  length  of  duration  in  hours 
and  minutes.  As  that  year  was  the  foggiest  known 
on  the  Pacific  Coast,  as  well  as  in  San  Diego,  it  will 
be  interesting  to  examine  the  data  in  detail.  There 
were  thirty-eight  days  with  one  hour  or  more  of 


22       Climate  and  Weather  oj  San  Diego 

fog,  or  a  total  of  188  hours,  making  an  average 
of  five  hours'  duration  for  each  foggy  day.  The 
month  with  the  longest  duration  was  October, 
with  a  total  of  eighty-nine  hours,  and  there  was 
some  fog  during  all  the  other  months  of  the  year, 
except  July. 

TABLE  III. — Number  Hours  of  Fog  in  October,  ign.    (The  month 
with  greatest  Jog  record) 

1  A.M 14    I  P.M O 

2  A.M 2O    2  P.M O 

3  A.M 21     3  P.M O 

4  A.M 21    4  P.M I 

5  A.M 20    5  P.M 2 

6  A.M 17    6  P.M 2 

7  A.M 8    7  P.M 6 

8  A.M 4    8  P.M 8 

9  A.M 2    9  P.M 9 

10  A.M O   IO  P.M IO 

11  A.M O   II  P.M 12 

Noon o     Midnight 12 

The  hours  of  greatest  frequency  were  between 
eleven  at  night  and  six  in  the  morning.  No  fog 
occurred  in  the  daytime  between  ten  and  four 
o'clock. 

The  beneficial  effect  of  fog  on  the  coast  of  south- 
ern California  is  apparent  to  anyone  who  has  lived 
a  year  in  this  region.  From  the  nature  of  the  con- 
densation it  is  impossible  to  measure  accurately 
the  amount  of  moisture  conveyed  by  fog.  There 
is  no  doubt  that  over  a  region  covered  by  vegetation 
exposing  a  natural  condensing  surface,  such  as 
eucalyptus,  palm,  ice  plant,  etc.,  not  less  than  a  ton 
of  water  to  the  acre  is  thus  distributed  during  the 
prevalence  of  every  dense  fog.  Fogs  not  only  supply 
considerable  moisture  to  growing  plants  and  trees, 
but,  owing  to  the  saturation  of  the  air,  evapo- 


Fog  23 

ration  is  at  a  standstill.  In  the  interest  of  the  law 
of  compensation  it  would  be  interesting  to  prove  a 
relationship  between  years  of  dense  fog  and  like 
periods  of  scanty  rainfall;  but  accurate  fog  records 
do  not  extend  back  farther  than  1896,  and  fifteen 
years  is  too  short  a  period  to  permit  the  drawing 
of  satisfactory  conclusions. 


CHAPTER  VII 
THE  RAINY  SEASON  IN  SAN  DIEGO 

THERE  is  considerable  misunderstanding  on 
the  part  of  the  non-resident  and  recent 
arrival  as  to  the  amount,  distribution,  and 
character  of  the  rains  in  southern  California.  It  is 
often  stated  by  a  resident  of  another  locality,  "It 
never  rains  in  San  Diego!'*  while  another  will  assert, 
"I  never  knew  it  to  rain  harder  than  at  San  Diego." 
Rainfall  statistics  for  the  past  sixty  years  will  show 
that  there  is  some  truth  in  both  statements.  San 
Diego  has  passed  through  a  year  with  but  three 
inches  of  rain,  an  amount  which  often  falls  in  a 
single  day  elsewhere  in  the  United  States;  and  this 
city  once  received  nearly  twenty-eight  inches  of  rain 
in  a  year.  An  examination  of  the  rainfall  statistics 
for  this  locality  shows  that  the  rainfall  is  chiefly 
remarkable  for  its  irregularity  in  amount.  Taking 
ten  inches  as  the  seasonal  average,  we  have  thirty- 
six  years  when  it  was  less  than  ten  inches,  and 
twenty-four  years  when  it  was  more.  In  the  two 
generations  which  have  passed  since  the  rain-gage 
was  first  set  up  in  old  San  Diego,  not  one  year  was 
like  any  preceding  or  following.  On  the  contrary, 
the  variation  between  the  greatest  and  the  least 
annual  rainfall  amounts  to  800  per  cent.  The  amount 
of  rain  is  thus  seen  to  be  the  least  dependable  of  all 
climatic  features  in  this  locality. 

In  the  distribution  of  rain  throughout  the  year  it 
will  be  seen  that  the  rainy  season  generally  begins 
in  October.  Over  the  greater  part  of  the  United 

(24) 


jRainy  Season  in  San  Diego  25 

States  there  are  no  well-marked  wet  or  dry  seasons; 
but  on  the  Pacific  Coast  very  little  precipitation 
occurs  between  the  middle  of  May  and  the  middle 
of  October.  The  following  summary  is  from  sixty- 
years  of  observations,  and  represents  average  condi- 
ditions: 

TABLE  IV. — Average  Number  of  Rainy  Days. 

Rainfall     Rainy  Rainfall     Rainy 

Inches        Days  Inches        Days 

January 1.76 6      July o.oo o 

February 1.96 7       August 0.06 I 

March 1.46 7       September o.i i 2 

April 0.61 5       October 0.08 3 

May 0.34 3       November 0.34 3 

June 0.06 i       December i  .83 6 

In  the  above  table  the  rainfall  is  in  inches,  which 
means  so  many  inches  in  depth  of  water  ^  on  an 
average  area.  A  "rainy  day"  is  one  on  which  one 
one-hundredth  of  an  inch  or  more  of  rain  falls.  One 
one-hundredth  of  an  inch  is  the  smallest  amount 
which  can  be  measured,  and  it  will  be  seen  from  the 
table  that  San  Diego  has  an  average  of  forty-four 
such  days  in  a  year.  If  we  consider  a  quarter  of  an 
inch,  this  locality  would  have  an  average  of  fourteen 
such  days  a  year,  and  one  inch  falls  on  an  average 
of  two  days  in  a  year.  Since  the  beginning  of  records, 
San  Diego  has  had  a  total  of  seven  days  when  the 
rain  exceeded  two  inches  in  any  consecutive  twenty- 
four  hours. 

The  character  of  the  rain  in  southern  California 
is  one  of  the  distinctive  features  of  the  climate. 
Drizzling  rains  are  uncommon,  as  mist  is  associated 
with  precipitation  only  when  the  storms  move  in 
from  the  southwest.  Nine-tenths  of  the  rain  in  this 
region  is  caused  by  the  low  areas  which  enter  the 


26       Climate  and  Weather  oj  San  Diego 

Oregon- Washington  coast  and  move  eastward.  Any 
southerly  deflection  of  these  storms  is  attended  by 
threatening,  rainy  weather.  A  question  often  asked 
is,  "If  the  storm  comes  from  the  north,  how  is  it 
that  our  rain-winds  are  always  southerly?"  A 
steady  southerly  wind  is  our  most  favorable  rain- 
wind,  because  the  circulation  of  the  winds  in  a  storm, 
or  "low"  area,  is  always  spirally  toward  the  center, 
and  with  a  direction,  when  viewed  from  above, 
opposite  that  of  the  hands  of  a  clock.  So  that,  as  a 
storm  drifts  eastward,  the  wind  veers  to  the  south- 
west and  west,  and  when  the  windvane  points  to 
the  northwest  we  know  that  the  rain  is  over,  for  the 
low  area  of  barometric  pressure  is  way  to  the  east- 
ward. This  explains  why  San  Diego  is  generally  the 
last  locality  on  the  Pacific  Coast  to  experience  a  rain, 
and  the  first  to  recover  from  its  effects. 

CAUSE  OF  RAIN 

The  average  person  seems  often  to  mistake  a 
mere  coincidence  for  a  cause,  and  to  give  it  no 
serious  thought.  It  is  not  strange,  then,  that  many 
have  placed  the  credit  of  rain  to  the  Japan  Current, 
to  the  Salton  Sea,  to  preceding  cold  or  warm  sum- 
mers in  this  region,  or  to  preceding  heavy  rains  in 
the  mountains  of  Arizona  or  New  Mexico.  Some 
have  even  gone  so  far  as  to  give  credence  to  the 
moon  or  to  the  movement  of  other  heavenly  bodies. 
The  manufacture  of  rain  to  order,  by  the  use  of 
explosives  or  gases,  is  still  believed  in  by  a  very  few 
uninformed  persons.  To  those  who  have  given 
much  thought  to  the  subject,  it  will  appear  that 
nature  accomplishes  results  on  such  a  vast  scale  that 


Rainy  Season  in  San  Diego  27 

even  the  more  plausible  causes,  such  as  ocean  cur- 
rents and  the  proximity  of  inland  bodies  of  water, 
would  not  explain  the  phenomena  of  rain.  As  shown 
in  detail  in  a  following  chapter,  the  Japan  Current, 
although  looming  large  on  popular  maps,  has  no 
effect  whatever  on  the  weather  over  California. 

Off  the  coast  of  California  the  surface-water  has 
a  southerly  drift  under  the  influence  of  the  strong, 
prevailing  northwesterly  winds  of  summer,  and  it 
has  a  northerly  movement  during  the  other  half  of  the 
year  owing  to  the  southerly  winds  of  winter.  It  is  thus 
seen  that  it  is  the  wind  which  sets  the  surface-water 
in  motion,  and  the  wind  is  caused  by  the  great 
atmospheric  eddies.  The  formation,  size,  and  drift 
of  these  aerial  eddies  are  caused  by  the  revolution 
and  inclination  of  the  earth,  and  the  distribution  of 
land-  and  water-masses.  The  Salton  Sea  myth, 
which  was  prevalent  a  few  years  ago,  has  now  lost 
prestige,  for  even  the  most  careful  observer  cannot 
see  any  connection  between  the  variation  of  the  size 
of  this  body  of  water  and  the  variable  rainfall  of 
southern  California.  It  would  be  a  great  satisfac- 
tion if  any  conection  could  be  traced  between  the 
local  rainfall  and .  preceding  warm  or  cold  summers 
in  San  Diego,  or  preceding  wet  or  dry  summer 
months  in  the  nearby  mountains  of  Arizona;  but 
graphic  curves  of  departure  from  the  normals  of 
temperature  and  precipitation  dp  not  show  coinci- 
dences, therefore  these  theories  will  have  to  be  aban- 
doned. As  to  the  effect  of  the  moon  or  stars  on  the 
weather,  or  the  existence  of  "equinoctial  storms," 
even  a  year's  residence  in  San  Diego  is  generally 
sufficient  to  convert  the  most  credulous  to  the  ver- 
dict of  the  meteorologist  that  there  is  nothing  in 


28       Climate  and  Weather  of  San  Diego 

these  theories,  attractive  though  they  be.  As  to 
the  manufacture  of  rain,  the  subject  may  be  dis- 
missed by  simply  stating  that  careful  laboratory 
experiments  show  no  relationship  between  con- 
cussion and  condensation. 

There  is  always  water-vapor  present  in  the 
atmosphere,  and  cloud,  fog,  mist,  or  rain  are  the 
various  degrees  of  condensation  of  vapor.  Air- 
moisture  is  reduced  to  liquid  water  only  by  decreas- 
ing temperature.  The  formation  of  rain  is  the  result 
of  cooling  by  expansion  against  surrounding  pres- 
sures as  the  air  ascends.  This  process  must  be  a 
continuous  one,  for,  should  all  the  vapor  present 
in  the  air  over  a  given  locality  be  condensed  at  one 
time,  the  result  under  the  most  favorable  conditions 
would  seldom  be  a  precipitation  of  more  than  two 
inches  of  rain.  A  continuous  process  is  caused  by 
the  circulation  of  the  air  in  an  aerial  eddy.  In  this 
aerial  eddy,  which  is  the  "low"  of  the  weather  map, 
there  is  a  radial  inflow  from  all  sides  and  an  ascen- 
sional movement  in  the  center.  Once  in  a  while 
heavy  showers  result,  when  the  relationship  between 
areas  of  high  and  low  pressure  is  such  as  to  cause 
cool,  northerly  winds  to  under-run  the  moisture- 
laden  sea  winds.  In  such  infrequent  instances  the 
moist  layer  of  air  flowing  above  the  other  is  cooled 
by  convection  in  the  same  way  that  it  is  when  it 
flows  up  and  over  a  mountain,  and  rain  follows. 


CHAPTER  VIII 

A  STUDY  OF  DRY  SEASONS  IN  SAN  DIEGO* 

^CONSIDERABLE  apprehension  has  been  felt 
1  j  as  to  the  outcome  of  the  present  season  in 
^^  San  Diego  as  regards  rainfall.  Twelve  years 
ago  similar  conditions  prevailed,  and  in  the 
"Monthly  Weather  Review"  of  January,  1900,  the 
editor  discussed  the  light  rainfall  in  San  Diego,  con- 
cluding with  this  statement: 

It  would,  however,  seem  that  there  is  little  likelihood 
that  the  rainfall  for  the  season  1899-1900  will  be  smaller 
than  four  inches,  so  that  the  three  seasons  just  past  will 
represent  nothing  worse  than  has  happened  twice  before 
in  ten  years,  namely,  between  1855  and  1860,  and  between 
1869  and  1872.] 

The  seasonal  rainfall  for  1899-1900  was  5.97 
inches,  or  1.97  inches  more  than  the  estimated 
amount. 

A  perusal  of  the  accompanying  table  will  show 
that  while  the  rainfall  to  date  has  been  scanty  it 
does  not  indicate  that  the  balance  of  the  season  will 
be  likewise  dry.  During  the  past  sixty-two  years 
San  Diego  has  experienced  six  other  years  when  the 
rainfall  was  less  than  that  which  has  fallen  so  far 
this  season.  The  record  of  these  dry  seasons  is  most 
instructive,  as  it  gives  us  the  only  indication  of  what 
may  be  expected  in  the  way  of  rain  for  the  next  few 

*By  the  author,  dated  February  3,  1912,  "Monthly 
Weather  Review,"  Vol.  XL,  pp.  121,  122. 

f'Monthly  Weather  Review,"  Vol.  XXVIII,  pp.  20,  21. 

(29) 


30       Climate  and  Weather  of  San  Diego 

months.  The  examination  of  average  conditions 
is  rarely  satisfactory  for  the  reason  that  the  normal 
seldom,  if  ever,  occurs.  With  this  fact  in  view,  the 
following  table  has  been  compiled  from  the  long 
rainfall  record  at  this  station.  Only  those  seasons 
which  resemble  the  present  one  have  been  considered. 

TABLE  V. — Rainjall  at  San  Diego,  California — Number  oj  Seasons 

in  Sixty-two  Years  Where  Less  Than  Half  the  Normal 

Was  Recorded  up  to  January  3 1 


Years 

Months 

Total, 
Oct.  i  to 
Jan.  31 

Oct. 

Nov. 

Dec. 

Jan. 

1863-64  

1872—73 

0.0 
.0 

.08 
.41 
.05 

:li 

.07 

.28 

0.73 

.0 

.04 
•39 

M 

.41 

.0 

.0 

0.04 
1.43 
.15 
.13 
.10 
.65 
.02 

•35 
1-39 

0.04 
.44 
1.05 
1.09 
.04 
.69 
1.70 

% 

0.81 
1.87 
1.32 

2.O2 
1.  14 
2.55 
2.4I 
.46 
2-33 

1876—77 

1882-83  

1886-87  

1800—  looo  .  . 

1901—02                    .  . 

IOO"}—  O4. 

191  1—  12 

Means  

•  17 

.38 

.47 

.64 

1.66 

Years 

Months 

Total, 
Oct.  i  to 
May  31 

Feb. 

March 

April 

May 

1863-64  

2.50 
4.21 
.18 

•95 

4.51 
.03 

1.57 
1.50 

O.2O 
.11 
1.44 
.41 
.02 

2.17 

O.OI 

.10 

.26 
.31 

^ 

.21 
•15 

1.25 
•03 

•43 
1.14 
•47 
1.45 
.06 

.12 

4-77 
6.32 
3.63 
4-83 
8.28 
5.82 
6.n 
4.40 

5.52 

1872—73.  . 

1876-77.  .  . 

1882-83   

1886-87 

i  800—  i  ooo 

1901-02  

1903-04  

191  I  —  12  

Means  

1.93 

.84 

.56 

.62 

-§ 


I  2 


U 


Dry  Seasons  in  San  Diego  31 

The  season  of  least  rainfall,  that  of  1876^77, 
showed  less  precipitation  than  any  of  the  previous 
twenty-seven  years,  and  nothing  has  approached  it 
in  the  thirty-five  years  that  have  elapsed.  The 
history  of  that  season  shows  that  the  last  rain 
occurred  on  March  9,  1876,  and  until  January  13, 
of  the  following  year  a  total  of  only  0.65  of  an  inch 
was  recorded.  There  appears  to  have  been  no  dam- 
age to  the  orchards  or  inconvenience  to  other  local 
interests,  as  the  water-storage  was  ample  for  all 
needs  at  that  time.  After  this  ten  months'  drought 
nearly  three  and  one-half  inches  of  rain  fell. 

It  will  be  observed  that  February  i  marks  the 
middle  of  the  rainy  season  in  San  Diego.  During 
a  normal  year  five  inches  of  rain  falls  after  this  date. 
In  a  dry  year,  like  the  present,  the  records  show  that 
nearly  four  inches  of  rain  is  liable  to  fall  between 
this  date  and  the  end  of  May. 

TABLE  VI.— Normal  Rainjall  by  Months 

September 0.06  March 1.70 

October 0.46  April 0.74 

November 0.83  May 0.41 

December i  .82  June 0.03 

January 2.00  July O 

February i  .96  August o 

Total 10.01 

During  the  dry  seasons  referred  to  above,  the 
February  rainfall  averages  1.93  inches,  generally 
falling  in  a  few  sharp  showers  accompanied  by  brisk 
to  high  southwesterly  winds.  In  the  cases  where 
the  March  rainfall  is  considerable,  like  the  years 
1877  and  1004,  the  showers  are  more  widely  scat- 
tered. In  ^  fact,  the  records  of  the^  weather  in  San 
Diego  during  droughty  periods  indicate  that  down- 


32       Climate  and  Weather  oj  San  Diego 

pours  are  common  in  February,  and  occur  during 
northerly  storms,  while  March  and  April  rains 
frequently  result  from  southerly  storms.  During 
May  the  rains  are  largely  of  the  "Sonora"  type, 
being  overflows  from  the  Arizona  disturbances. 
Rains  from  such  storms  often  follow  dense  fogs.  The 
character  of  the  weather  during  seasons  of  light 
rainfall  is  very  distinct  and  constitutes  a  class  by 
itself,  as  shown  by  the  pressure,  temperature,  winds, 
humidity,  etc.,  which  have  been  examined  for  each 
of  these  individual  seasons.  The  records  of  the  last 
few  dry  seasons  have  been  studied  in  connection 
with  the  daily  weather  map,  and  there  is  found  to  be 
a  striking  similarity  in  the  distribution  of  the  pres- 
sure-areas. The  past  seasons  resemble  the  present 
in  that  the  widespread  high  areas  are  persistent 
and  greatly  outnumber  the  lows  in  their  frequency, 
and  the  former  possess  far  more  energy.  While  it 
is  impossible  to  make  seasonal  forecasts,  a  perusal 
of  the  tables  which  accompany  this  article  would 
indicate  that  there  is  little  likelihood  of  San  Diego 
experiencing  a  severe  drought,  but  that,  on  the  con- 
trary, there  is  every  reason  to  believe  that  this 
region  will  receive  not  less  than  three  or  four  inches 
more  of  rain  during  this  season. 

NOTE. — No  rain  fell  during  the  month  of  February,  fol- 
lowing the  publication  of  this  article;  but  in  March  5.72 
inches  fell,  followed  by  2.13  inches  in  April. 


CHAPTER  IX 
THE  STABILITY  OF  THE  CLIMATE 

PERHAPS  one  of  the  most  frequent  remarks 
concerning  the  weather  is  positive  assurance 
from  some  of  the  oldest  inhabitants  that  the 
climate  is  changing.  It  is  their  conviction  that  the 
seasons  are  becoming  drier  or  wetter,  or  that  it  is 
colder  or  warmer  than  it  used  to  be.  That  the  cli- 
mate is  changing  cannot  be  denied;  but  this  change 
is  one  covering  thousands  of  years,  and  it  is  not 
compassed  by  the  little  span  of  recorded  history. 
Though  thousands  of  years  have  elapsed  since  the 
ice-sheet  began  its  retreat,  we  have  to  go  but  a  few 
hundred  miles  to  the  Yosemite  National  Park  to  see 
regions  not  yet  beyond  the  glacial  conditions  of  that 
epoch.  It  is  thus  seen  that  we  are  experiencing  a 
phase  of  climatic  oscillations  which  had  its  beginning 
many  thousands  of  years  ago.  Climates  change 
from  age  to  age,  but  the  systematic  record  of  past 
events  is  limited  to  so  short  a  space  of  time  that  no 
change  has  been  observed,  and  no  general  increase 
or  decrease  either  in  temperature  or  rainfall.  There 
are  unquestioned  secular  fluctuations  in  climate, 
but  the  range  of  these  undulations  is  probably  over 
a  generation  long,  and  then  they  cover  but  a  few 
inches  in  rainfall  or  a  few  degrees  of  temperature. 
It  seems  a  far  cry  back  to  the  golden  days  of  '49, 
when  the  San  Diego  rain-gage  was  set  up  in  the  old 
Spanish  mission;  but  how  many  hundred  times 
fifty  years  have  elapsed  since  the  days  when  the  lava 
met  the  sea  at  Point  of  Rocks  at  the  Mexican 

(33) 


34       Climate  and  Weather  of  San  Diego 

boundary?    One  is  a  historic  period  and  the  other 
is  a  geologic  epoch. 

The  highest  point  reached  in  the  annual  tempera- 
ture line  of  the  above  table  is  63.8  degrees  in  1867, 
and  the  lowest  was  in  1894,  when  58.4  was  recorded. 
It  is  thus  seen  that  in  half  a  century  there  was  less 
than  six  degrees  difference  between  the  warmest 
and  the  coldest  years.  The  temperature  chart  is 
valuable,  not  because  it  presents  periodic  fluctua- 


San  Diego  Annual  Temperatures  for  Fifty-nimYears 


50 


i 


i 


601 
55°. 


.65° 


.60 
55° 


Diagram  of  annual  temperatures  for  fifty-nine  years 

tions,  but  only  in  that  it  shows  the  slight  range  in 
temperature  from  year  to  year  in  San  Diego  since 
1852.  Mean  annual  temperatures  for  purposes  of 
comparison  are  misleading,  as  they  may  be  used  to 
imply  relationship  where  none  exists.  For  example: 
The  average  annual  mean  temperature  of  San  Diego 
is  6 1  degrees,  which  happens  to  be  the  same  as 
Atlanta,  Georgia;  but  the  thermometer  at  the  latter 
city  has  climbed  nearly  10  degrees  higher  than  that 
of  San  Diego,  and  has  dropped  40  degrees  lower. 

In  the  rainfall  chart,  the  year  was  made  to  end 
June  30,  so  as  to  conform  more  nearly  to  the  sea- 


The  Stability  oj  the  Climate 


35 


sonal  distribution.  Eighty  per  cent  of  the  annual 
rainfall  of  San  Diego  falls  between  November  of  one 
year,  and  March  of  the  next.  The  average  amount 
is  9.62  inches.  The  season  recording  the  greatest 
amount  of  rain  was  that  of  1883-1884,  when  25.97 
inches  of  rain  fell.  The  season  of  least  rain  was  that 
of  1876-1877,  when  3.75  inches  were  recorded.  A 


San  Diego  Seasonal  Rainfall  for  Sixty- two  Years 


Seasonal  Rainfall  Chart  for  sixty-two  years 

close  inspection  of  this  chart  shows  that  the  driest 
period  ever  known  extended  from  1869  to  1872, 
when  the  rainfall  averaged  4.5  inches  a  season. 
The  precipitation  (rain  and  melted  snow)  increases 
back  from  the  coast,  so  that  within  twenty-five  miles 
of  the  city  of  San  Diego  the  annual  seasonal  rainfall 
is  five  or  six  times  greater.  It  will  thus  be  seen  that 
even  during  this  four  years'  dry  period  there  fell, 


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38       Climate  and  Weather  of  San  Diego 

TABLE  VIII— Showing  Highest  and  Lowest  Temperatures  Regis- 
tered During  each  Month  Jrom  January,  1874,  to  June  30,  1912, 
at  San  Diego,  Calijornia. 


YEAR 

Jan. 

Feb. 

March 

April 

May 

June 

. 

1 

52 
52 
50 
50 
50 
51 
48 
47 
46 
51 
48 
45 
47 
52 
50 
48 
52 
50 
46 
53 
47 
49 
45 
51 
48 
50 
51 
48 
49 
51 
50 
50 
48 
48 
50 
51 
47 
50 
46 
49 
49 

H 

• 

c 

i 

1 

S 

ii 

S 

2 

43 
42 
43 
39 
43 
44 
44 
45 
42 
51 
43 
42 
45 
47 
45 
44 
47 
47 
45 
44 
41 
43 
43 
44 
42 
46 
45 
46 
45 
46 
47 
47 
44 
44 
42 
43 
46 
46 
47 
44 
45 

1872  
1873  
1874 

73 
75 
71 
68 
65 
78 
68 
76 
73 
70 
64 
76 
78 
68 
74 
74 
64 
78 
66 
76 
75 
80 
69 
77 
77 
73 
78 
74 
79 
75 
81 
78 
83 
73 
72 
73 
80 
70 
76 
77 
82 

37 
44 
42 
42 
39 
42 
38 
35 
32 
36 
34 
32 
39 
38 
35 
38 
33 
36 
35 
35 
38 
38 
32 
36 
39 
40 
36 
43 
46 
40 
36 
43 
36 
46 
35 
35 
44 
42 
34 
41 
40 

68 
77 
64 
70 
77 
75 
69 
74 
63 
82 
70 
83 
79 
76 
80 
76 
67 
85 
77 
70 
68 
75 
69 
82 
83 
76 
75 
76 
76 
83 
71 
75 
68 
79 
76 
84 
68 
74 
72 
70 
74 

44 
37 
41 
44 
39 
45 
44 
38 
35 
39 
37 
36 
38 
40 
44 
38 
42 
37 
38 
34 
42 
40 
34 
39 
39 
38 
42 
34 
45 
44 
39 
35 
41 
40 
47 
41 
37 
41 
37 
34 
43 

71 
72 
63 
71 

75 
70 
68 
99 
69 
72 
79 
71 
68 
81 
68 
82 
72 
80 
74 
76 
73 
75 
72 
74 
85 
70 
77 
86 
80 
82 
76 
72 
74 
76 
80 
82 
78 
74 
84 
77 
71 

44 
40 
41 
39 
43 
48 
42 
44 
38 
40 
39 
48 
43 
42 
41 
44 
41 
45 
41 
41 
44 
40 
36 
38 
41 
40 
38 
44 
46 
47 
43 
42 
44 
38 
41 
40 
42 
42 
45 
44 
45 

74 
82 
71 
77 
87 
67 
77 
82 
80 
82 
70 
85 
69 
83 
71 
80 
93 
83 
85 
77 
80 
78 
83 
81 
74 
88 
86 
93 
67 
66 
69 
73 
78 
68 
88 
75 
83 
82 
96 
79 
67 

83 
78 
74 
82 
76 
68 
73 
94 
84 
72 
73 
89 
72 
73 
72 
79 
70 
80 
75 
67 
87 
88 
72 
80 
98 
67 
69 
66 
75 
67 
78 
68 
69 
77 
70 
73 
68 
87 
75 
74 
72 

80 
75 
76 
77 
88 
94 
76 
93 
73 
76 
75 
84 
81 
74 
75 
78 
76 
72 
93 
78 
75 
75 
73 
77 
89 
70 
88 
70 
87 
86 
76 
74 
74 
70 
89 
80 
70 
77 
71 
91 
72 

55 
58 
52 
53 
51 
55 
51 
52 
52 
53 
55 
56 
50 
52 
54 
54 
54 
56 
51 
53 
51 
53 
50 
51 
54 
54 
54 
55 
56 
53 
52 
54 
56 
54 
53 
52 
50 
53 
54 
53 
54 

1875.  . 

1876.... 

1877  

1878  
1879 

1880.  . 

1881. 

1882  

1883  
1884 

1885  
1886 

1887... 

1888  
1889  
1890  
1891 

1892.. 

1893 

1894  

1895  
1896  

1897..  .. 

1898 

1899  
1900  
1901 

1902  

1903  
1904 

1905. 

1906  
1907  

1908  
1909  
1910  

1911  
1912  

The  Stability  oj  the  Climate 


39 


TABLE  VIII. — Showing  Highest  and  Lowest  Temperatures  Regis- 
tered During  each  Month  from  January,  1874,  to  June  30,  1912, 
at  San  Diego,  California,  continued. 


YEAR 

July 

August 

Sept. 

October 

Nov. 

Dec. 

M 
e» 

a 

9 

M 

.S 

3 

.5 

H 

c 
S 

H 

c 

ii 

1 

.S 

1872  
1873. 

75 
77 
79 
79 
78 
86 
77 
75 
73 
80 
78 
80 
84 
82 
81 
79 
77 
84 
80 
88 
75 
79 
77 
74 
80 
79 
77 
78 
84 
74 
76 
78 
76 
74 
82 
81 
80 
79 
82 
93 

58 
60 
59 
61 
60 
59 
56 
58 
54 
57 
57 
59 
54 
58 
57 
60 
55 
59 
56 
58 
57 
57 
57 
57 
56 
59 
60 
57 
60 
57 
55 
59 
59 
59 
58 
59 
56 
58 
56 
59 

86 
78 
83 
83 
81 
82 
80 
81 
84 
82 
83 
84 
92 
89 
82 
77 
82 
89 
89 
85 
80 
81 
90 
78 
88 
89 
83 
76 
80 
79 
79 
85 
82 
88 
78 
75 
79 
93 
82 
84 

60 
63 
56 
63 
60 
58 
55 
54 
56 
56 
62 
60 
54 
62 
61 
54 
57 
62 
58 
60 
57 
59 
55 
54 
59 
60 
63 
58 
59 
58 
60 
60 
63 
58 
57 
60 
60 
59 
58 
58 

80 
82 
78 
88 
82 
91 
100 
92 
82 
86 
80 
101 
78 
90 
78 
79 
82 
91 
83 
89 
80 
77 
90 
90 
80 
83 
91 
92 
87 
72 
73 
83 
86 
81 
91 
79 
84 
100 
86 
76 

54 
55 
54 
57 
54 
58 
53 
54 
50 
52 
50 
59 
51 
56 
60 
58 
58 
54 
60 
55 
54 
53 
52 
54 
54 
58 
56 
55 
53 
56 
56 
56 
56 
55 
58 
50 
52 
53 
56 
54 

87 
76 
90 
88 
80 
73 
87 
92 
81 
72 
81 
80 
87 
88 
75 
85 
80 
80 
90 
84 
83 
88 
87 
84 
79 
76 
81 
93 
72 
96 
71 
84 
94 
85 
89 
78 
80 
94 
87 
84 

45 
49 
46 
53 
48 
47 
44 
46 
48 
46 
49 
48 
47 
47 
47 
50 
53 
52 
49 
50 
46 
50 
45 
54 
52 
51 
51 
48 
50 
51 
52 
51 
53 
50 
46 
54 
48 
49 
50 
50 

81 
85 
75 
78 
79 
78 
77 
79 
78 
76 
80 
82 
74 
76 
77 
82 
75 
83 
91 
82 
84 
83 
78 
85 
76 
83 
76 
81 
89 
80 
74 
84 
93 
80 
86 
86 
76 
85 
74 
82 

42 
49 
45 
50 
43 
46 
40 
43 
40 
38 
42 
43 
42 
42 
40 
44 
46 
46 
46 
44 
40 
40 
45 
38 
43 
45 
43 
50 
51 
49 
42 
45 
48 
44 
39 
45 
42 
42 
43 
44 

72 
68 
82 
75 
77 
78 
79 
71 
77 
77 
78 
78 
68 
79 
76 
74 
73 
69 
79 
72 
71 
82 
70 
79 
76 
80 
79 
80 
79 
76 
74 
75 
78 
74 
80 
79 
69 
71 
74 
78 

40 
44 
39 
38 
43 
40 
35 
32 
40 
39 
41 
42 
36 
40 
40 
36 
44 
40 
47 
32 
36 
38 
41 
34 
46 
36 
43 
46 
44 
35 
40 
44 
44 
38 
41 
43 
37 
36 
40 
36 

1874  

1875  
1876 

1877  

1878  
1879  
1880  
1881 

1882  
1883  
1884  
1885  

1886  
1887 

1888. 

1889 

1890. 

1891  
1892  
1893  
1894  

1895  
1896  
1897. 

1898  

1899 

1900  

1901.  ... 

1902... 

1903  
1904  
1905  
1906  
1907 

1908. 

1909 

1910  

1911.... 
1912  

40       Climate  and  Weather  of  San  Diego 

within  a  short  distance  of  San  Diego,  not  less  than 
an  average  of  twenty-five  inches  of  rain.  Strictly 
scientific  conservation  of  this  dependable  precipita- 
tion will  insure  an  ample  and  stable  water-supply 
for  San  Diego  and  vicinity. 


CHAPTER  X 
THE  EQUABILITY  OF  THE  CLIMATE 

THE  climate  of  San  Diego  is  characterized  by 
uniformity  of  temperature  and  invariability 
of  sunshine.  The  temperature  covers  a  short 
range,  and  the  sunshine  is  even  more  constant  in 
winter  than  in  summer.  San  Diego  may  truthfully 
be  said  to  have  the  shortest  thermometer  in  the 
United  States,  with  one  exception  (the  southeast 
Farallone  Island).  These  statements  are  accepted  by 
the  meteorologist  from  his  comparative  studies  of 
other  climates,  and  by  the  resident  as  a  matter  of 
almost  unconscious  observation;  only  to  the  non-resi- 
dent do  these  facts  appear  almost  beyond  belief. 

The  chief  cause  of  San  Diego's  salubrity  of  climate 
lies  in  its  latitude.  Among  other  causes  are:  Its 
location  to  the  leeward  of  the  ocean,  its  distance 
from  the  eastward-moving  storms  of  the  northern 
coast,  and  the  absence  of  mountains  close  to  the  sea. 
The  latitude  gives  a  temperate  climate,  the  proximity 
to  the  sea  equability  of  temperature,  the  distance 
from  the  storm-tracks  freedom  from  high  winds  and 
rough  weather,  and  the  absence  of  mountains  in 
the  immediate  neighborhood  contributes  to  infre- 
quent cloud  or  fog. 

INFREQUENCY  OF  HOT  AND  COLD  PERIODS 

The  most  severe  test  which  can  be  applied  to  any 
climate  is  an  examination  of  the  extremes  of  weather 
conditions  as  they  appear  in  a  long,  unbroken, 

(41) 


42       Climate  and  Weather  oj  San  Diego 

automatic  record.  From  a  study  of  half  a  century 
of  the  weather  conditions  in  San  Diego,  it  is  found 
that  the  average  of  the  three  consecutive  warmest 
days  was  82.9  degrees,  occurring  in  September,  and 
the  average  of  the  three  consecutive  coldest  days 
was  40.2  degrees,  recorded  in  January.  For  twenty- 
five  years  the  temperature  has  been  continuously 
recorded  by  automatic  instruments,  and  during 
this  period  the  thermometer  has  been  lower  than  80 
degrees  on  an  average  of  364  days  a  year.  The 
extremes  at  San  Diego  are  101  and  32  degrees.  The 
thermometer  touched  90  degrees  on  an  average  of 
four  hours  a  year,  and  dropped  to  40  degrees  or 
lower  on  an  average  of  10  hours  a  year.  The  aver- 
age daily  range  of  the  thermometer  is  13  degrees. 
The  average  difference  between  the  mean  tempera- 
ture of  one  day  and  that  of  the  next  is  2  degrees. 
San  Diego  is  one  of  three  places  in  the  United 
States  where  the  thermometer  has  not  been  lower 
than  32  degrees,  viz,  Key  West,  southeast  Farallone, 
and  San  Diego.  Practical  illustrations  of  the  equabil- 
ity of  temperature  are  found  in  the  facts  that  only 
a  small  amount  of  fuel  is  used  locally  for  heating, 
and  but  little  more  ice  is  used  in  summer  than  in 
other  seasons  of  the  year. 

TABLE  IX. — The  Average  Highest  and  Lowest  Temperatures 
in  the  Year 

Mean         Mean  Mean         Mean 

Max.  Mm.  Max.  Min. 

January 62 44  July 74 61 

February 62 47  August 75 63 

March 63 50  September 74 . 


April 66 52       October 70 58 

May 68 55       November 68 52 

June 70 57       December 65 48 


The  Equability  of  the  Climate  43 

THE  SUN  SHINES  ON  AN  AVERAGE  OF  356  DAYS  A 
YEAR   IN   SAN   DIEGO 

Photographic  or  electric  sunshine  instruments 
have  faithfully  recorded  the  sunshine  in  San  Diego 
for  the  past  twenty  years,  and,  during  this  time, 
there  has  been  an  average  of  less  than  nine  days  a 
year  without  one  hour  or  more  of  sunshine.  Strange 
as  it  may  seem,  the  cloudiest  days  are  in  spring  or 
summer,  when  the  veto  cloud  effectually  screens  the 
sun's  rays,  causing  the  distribution  of  sunshine  to  be 
less  in  summer  than  in  winter. 

TABLE  X. — Per  Cent  oj  Possible  Sunshine 

January 67       July 67 

February 66       August 72 

March 64       September 73 

April 69       October 73 

May 58       November 76 

June 60       December 75 

Year 68 

Perusal  of  foreign  climatic  charts  gives  truth  to 
the  statement  that  the  coast  of  southern  California 
bears  the  same  relationship  to  America  that  the 
region  about  the  Mediterranean  does  to  Europe, 
and  what  the  Riviera  is  to  the  Mediterranean,  San 
Diego  is  to  southern  California. 


CHAPTER  XI 
CLIMATIC  FACTORS  IN  BUILDING 

AS  affecting  residence,  local  variation  in  climate 
/"%    is  one  of  the  most  interesting  studies,  for  San 
Diego,  like  all  regions  with  climatic  advan- 
tages, has  well-marked  general  and  specific  varia- 
tions.   These  variations  are  caused  by  exposure  to 
the  sun  and  wind,  drainage  of  air  as  well  as  water, 
and  elevation. 

One  of  the  first  errors  to  be  corrected  is  a  mis- 
apprehension of  the  general  character  of  the  climate 
as  regards  temperature.  It  must  be  remembered 
that  the  climate  of  San  Diego  is  not  tropical,  nor 
even  semi-tropical,  but  that  it  is,  in  every  meaning 
of  the  word,  a  temperate  climate.  We  soon  learn 
that  we  cannot  wear  the  clothing  of  the  semi- 
tropics,  that  our  houses  have  to  be  heated  in  winter, 
that  in  summer  out-of-door  porches  for  lounging 
are  nearly  useless,  because  of  the  cool  evenings,  and 
that  lawns  are  made  for  looks  and  not  for  use.  A 
frequent  question  asked  during  the  summer  as  well 
as  the  winter  is,  "When  does  it  get  warm  in  San 
Diego?"  San  Diego  is  relatively  warm  or  cool;  that 
is,  it  is  warm  in  winter  and  cool  in  summer,  by  com- 
parison with  other  places  in  the  United  States.  For 
example,  the  early  part  of  the  year  1912  was  mild 
throughout  the  entire  United  States,  yet  the  cool 
mornings  and  nights  prompted  many  to  ask  where 
they  could  go  for  a  warmer  climate.  In  nearly 
every  instance  where  the  daily  telegraphic  tempe- 
ratures were  compared,  San  Diego  was  shown  to 

(44) 


Climatic  Factors  in  Building  45 

have  the  highest  minimum  temperature.  San  Diego 
has  a  cool  climate  throughout  the  year,  and  yet  with 
these  moderate  temperatures  semi-tropical  plants 
have  uninterrupted  growth.  It  is  one  of  the  rare 
localities  where  northern  and  southern  vegetation 
flourish  side  by  side.  In  many  gardens  pines  and 
palms  fraternize,  banana  and  lemon  trees  blossom 
and  bear  during  all  the  months  of  the  year,  and  there 
are  rose  bushes  that  have  been  covered  with  flowers 
every  day  for  a  dozen  years  or  more.  With  this 
proof  of  the  absence  of  killing  frost  there  is  still  a 
tonic  in  the  air,  a  bracing  quality  compounded  of  a 
moderately  high  percentage  of  moisture  and  com- 
paratively low  temperature.  This  feature  is  unknown 
in  other  southern  regions,  and  puts  at  rest  all  fears 
of  San  Diego  having  an  enervating  climate. 

There  are  few  cities  of  its  size  in  the  United  States 
where  so  much  building  is  constantly  going  on  as  in 
San  Diego.  In  southern  California  there  need  be  no 
delay  in  building  operations,  for  there  are  no  inter- 
ruptions on  account  of  weather  conditions.  Those 
contemplating  building  a  residence  here  should 
carefully  consider  the  position  of  the  building-site, 
its  exposure  to  the  sun  and  wind,  elevation,  and 
character  of  the  soil.  As  a  rule,  view  lots  are  windy 
ones.  But,  although  the  house  fronts  the  west, 
which  for  some  reasons  is  the  best  frontage,  the  south 
and  east  sides  can  be  arranged  to  admit  the  sun- 
shine and  drier  winds.  The  location  of  a  residence 
in  this  locality  with  relationship  to  the  prevailing 
winds  is  of  considerable  consequence.  In  the  chapter 
on  Humidity  will  be  found  a  diagram  showing  the 
frequency  of  wind-direction  and  humidity.  This 
diagram  should  be  useful  to  constructors.  Air- 


46       Climate  and  Weather  of  San  Diego 

drainage  must  be  considered  apart  from  the  general 
winds,  although  in  canons  and  valleys  the  down- 
rushing  air  of  evening  and  the  up-rushing  air  of 
morning  appear  to  the  observer  as  an  ordinary  cold 
breeze. 

Cold  air  flows  down  hill,  and  a  location  in  a  hollow 
or  in  a  depression  on  a  hillside  is  to  be  avoided 
because  of  this  fact,  and  because  of  the  accumula- 
tion of  cold  air  in  such  pockets.  Owing  to  such  a 
flow  of  air  it  is  much  better  to  build  a  little  beyond 
the  brow  of  a  hill  than  on  the  hillside  or  on  the 
immediate  crest. 

SUNSHINE  AND  VENTILATION 

In  Rome,  rooms  with  a  southern  or  eastern 
exposure  command  a  much  higher  rent,  being  more 
desirable  on  account  of  the  sunshine.  Exposure  to 
the  sun  in  San  Diego  is  no  less  beneficial;  and  the 
importance  of  giving  a  house  full  access  to  the  sun's 
rays  is  equal  only  to  the  exposure  of  the  house  with 
relation  to  the  prevailing  winds.  The  ideal  house  is 
one  with  the  east,  southeast,  and  south  sides  mostly 
of  glass.  Such  an  arrangement  does  away  with  much 
artificial  heating.  A  building  is  best  warmed  by  a 
furnace,  steam-radiator,  or  open  grate;  oil  or  gas 
heating  stoves  are  not  hygienic  unless  a  room  is 
thoroughly  ventilated.  Ventilation  is  especially 
important  in  San  Diego  because  there  is  little  daily 
change  in  atmospheric  pressure.  This  is  quickly 
noticed  in  going  into  a  closed  room  where  the  air 
is  found  to  be  "stale."  If  the  occupants  are  in  good 
health,  the  temperature  of  a  room  may  safely  be 
kept  not  over  10  or  15  degrees  above  the  outside 


Climatic  Factors  in  Building  47 

air  in  December,  January,  and  February.  From 
March  to  November  the  air  of  the  living-room 
should  correspond  closely  with  the  outside  air- 
temperature. 

As  a  climatic  factor,  elevation  above  sea-level 
is  not  so  important  here  as  elsewhere.  Altitude 
gives  the  advantage  of  less  moisture,  but  the  dis- 
advantage of  more  wind.  This  may  not  seem  true 
ordinarily,  but  it  should  be  remembered  that  San 
Diego  is  a  seaport  and,  consequently,  has  a  higher 
average  wind  velocity  than  interior  towns.  While 
low  elevation  always  accompanies  more  or  less 
stagnant  air,  there  is  a  compensation  in  less  range 
of  temperature  between  night  and  day.  ^ 

Another  feature  which  should  be  given  careful 
consideration  is  solidity  of  foundation.  This  may 
seem  to  appear  of  minor  importance  now,  but  it  is 
well  to  take  precautionary  measures  for  the  future. 
The  foundations  of  structures  should  go  down  to 
natural  earth;  that  is,  "fills"  should  be  penetrated 
to  the  underlying  hardpan.  All  "made"  ground  is 
subject  to  settling,  and,  owing  to  its  nature,  it  is  in 
a  state  of  unstable  equilibrium. 


CHAPTER  XII 

THE  COAST,  MOUNTAIN,  AND  DESERT  CLIMATES 
OF  SAN  DIEGO  COUNTY 

WHILE  much  has  been  written  about  the 
equability  of  the  climate  of  San  Diego  Bay 
region,  little  has  been  said  about  the  great 
diversity  of  climate  to  be  found  within  the  limits  of 
the  county.  Some  of  the  contrasts  in  temperature 
and  precipitation  within  this  relatively  small  area 
are  so  great  that,  without  the  authority  of  govern- 
ment statistics,  they  would  appear  impossible.  The 
Chinese  empire  has  been  called  "the  paradise  of  the 
man  with  the  long-bow,"  because,  as  a  Chinaman  is 
loth  to  collect  statistics,  it  allows  the  traveler  to 
invent  almost  any  tale,  as  it  cannot  be  contradicted 
by  available  data.  This  is  not  so  in  San  Diego,  for 
it  is  a  matter  of  history  that,  after  the  landing  of 
Fremont's  troops  in  the  late  forties,  reliable  weather 
records  were  commenced  and  have  been  maintained 
ever  since. 

It  is  upon  such  statistics  that  the  following 
account  of  the  varying  climatic  conditions  is  based: 

SAN   DIEGO   COUNTY   HAS  THREE   DISTINCT   CLIMATES 

t  There  are  three  distinct  climates  to  be  found 
within  the  limits  of  San  Diego  County.  They  are: 
First,  the  nearly  sub-tropical  coast  climate  of  the 
San  Diego  Bay  region;  second,  the  climate  of  the 
mountainous  district  a  score  of  miles  back  from  the 
coast;  and  third,  the  desert  climate  another  score 

(48) 


Coast,  Mountain,  and  Desert  Climates     49 


TABLE  XI. — Son  Diego  County  Data.   Temperature,  Precipitation, 
and  Character  oj  Weather* 


oj 

R 

d 

ElCajon 

1 

Mammoth  f 
Tank 

1 

I 

C/5 

Average  Temperature 

Degrees 
Fahr. 
37  0 

Degrees 
Fahr. 
53  8 

Degrees 
Fahr. 
49  6 

Degrees 
Fahr. 
53  9 

Degrees 
Fahr. 
48  0 

Degrees 
Fahr.t 
54  0 

February  

36  1 

52  8 

52.0 

58.9 

49.5 

54  6 

March 

39  9 

55  7 

54  3 

66  1 

52  4 

56  2 

April  

43  9 

58  2 

58.3 

75.4 

55  8 

58  2 

May 

49  5 

62  4 

62  6 

83  6 

60  6 

60  8 

June  

60  7 

67  2 

67.9 

92.5 

65.1 

63  8 

Julv 

65  0 

71  3 

72  5 

98  5 

68  9 

66  9 

August  

64  5 

71.0 

72.1 

96.8 

69  6 

68.7 

September  
October  

59.0 
49  6 

69.0 
64.2 

69.0 
61.5 

90.0 
76.8 

65.9 
59.4 

66.9 
63  0 

44  7 

60  1 

55  1 

63  8 

53  5 

59  0 

December  

38  7 

54.6 

49.5 

55.4 

51.1 

55  7 

49  0 

61  7 

60  4 

76.0 

58  3 

60  6 

Mean  precipitation  (rain 
ana  melted  snow) 
July  

Inches 
0  27 

Inches 
0  10 

Inches 
0  01 

Inches 
0.06 

Inches 
0.04 

Inches 
0.06 

August       

0  64 

0  11 

0  08 

0  34 

0  03 

0  11 

September  

0  60 

0.12 

0.08 

0.04 

0.08 

0.08 

October     

1  76 

0  50 

0  53 

0.11 

0  50 

0  34 

November  
December  

3.35 
5  07 

1.39 
1  28 

1.24 
1  35 

0.11 
0.35 

1.22 
1.88 

0.95 
1.83 

6  98 

2  43 

3  86 

0  16 

3  19 

1  76 

February  .  .  . 

7  88 

2  67 

2  80 

0.52 

2.64 

1.96 

March 

7  97 

2  71 

3  02 

0  20 

2  65 

1  46 

April  

2  30 

0  63 

0  85 

0.09 

1.13 

0.61 

May              .... 

2  19 

0  44 

0  64 

0  02 

0  54 

0  34 

June  

0  25 

0  11 

0  10 

0.07 

0.06 

Seasonal     

40  07 

12  94 

15  21 

2  02 

13  96 

9  62 

38  84 

12  24 

15  15 

1  99 

13  79 

9  54 

State  of  weather 
Rainy  , 

Aver. 

days 
60 

Aver, 
days 
44 

Aver. 

dT 

Aver. 

days 

Aver. 

d$s 

Aver, 
days 
43 

Clear  

220 

266 

143 

292 

240 

266 

Partly  cloudy 

79 

59 

191 

22 

66 

49 

Cloudy... 

66 

40 

31 

51 

59 

50 

Wind 

W 

SW 

W 

W 

W 

NW 

*Section  13,  "Summary  of  Climatological  Data  for  the  United  States.'* 

tNormal  temperature  for  thirty-three  years. 

NOTE. — The  elevations  at  which  these  observations  were  made  are  as 
follows:  Cuyamaca,  4.677  feet;  El  Cajon,  482  feet;  Escondido.  657  feet; 
Mammoth  Tank,  257  feet;  Poway,  460  feet;  San  Diego,  93  feet. 


50       Climate  and  Weather  of  San  Diego 

of  miles  farther  east.  The  seasonal  distribution  of 
precipitation  and  the  usually  clear  skies  are  com- 
mon to  all  of  southern  California.  A  brief  classifi- 
cation would  give  the  immediate  San  Diego  Bay 
region  cool  summers  and  warm  winters;  slight  vari- 
ation in  temperature  from  day  to  night;  slight  but 
steady  wind  movement;  moderately  high  relative 
humidity,  and  frequent  rainfall  in  limited  amounts. 


Percentage  of 
Direction 


Diagram  of  relative  wind  velocity  and  frequency 

The  mountainous  region  of  San  Diego  County  has 
warm  summers  and  cool  winters;  considerable  range 
between  day  and  night  temperatures;  fresh  daylight 
winds;  low  relative  humidity,  and  moderately  heavy 
winter  rains  supplemented  by  summer  thunder- 
storms. The  desert  climate  of  this  region  is  the 
most  perfect  exponent  of  its  type,  being  notable  for 
constant  and  unvarying  sunshine;  warm  winters, 
with  great  variation  between  night  and  day  tem- 
peratures; hot  summer  days  without  cool  nights; 


Coast,  Mountain,  and  Desert  Climates     51 


extremely   low   relative   humidity;  brisk  daylight 
winds,  and  practically  no  rainfall. 

The  principal  features  of  the  three  climates  are 
shown  graphically  in  the  following  diagrams.     In 


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Comparative  coast,  mountain  and  desert  temperatures, 
and  precipitation 


52       Climate  and  Weather  of  San  Diego 

these  diagrams  the  records  of  the  year  1902  are  used, 
as  that  year  more  nearly  approached  normal  condi- 
tions and  thus  facilitated  comparison.  The  city  of 
San  Diego,  with  an  elevation  of  93  feet,  is  taken  as 
representative  of  the  coast  climate;  Cuyamaca, 
with  an  elevation  of  4,677  feet  above  sea-level  best 
shows  the  mountain  climate;  and  the  desert  condi- 
tions at  Volcano  Springs  (now  within  the  contour  of 
Salton  Sink),  because  that  station  was  220  feet 
below  sea-level. 

It  is  perhaps  unnecessary  to  state  that  the  tem- 
peratures in  the  above  tables  were  all  made  with 
standard  Weather  Bureau  thermometers,  exposed  in 
ventilated  instrument  shelters,  and  therefore  show 
shade  temperatures.  In  the  desert  regions  it  is  not 
unusual  for  the  mean  monthly  temperature  to  aver- 
age 100  degrees,  while  on  the  coast,  at  San  Diego, 
there  have  been  periods  covering  three  consecu- 
tive years  (1891-93)  when  the  thermometer  failed  to 
register  so  high  as  90  degrees.  There  is  likewise  a 
remarkable  divergence  in  rainfall  between  continu- 
ous regions  of  mountain  and  desert.  Years  have 
passed  on  the  desert  without  so  much  as  a  few  inches 
of  rain,  yet  San  Diego  County  also  has  the  record  of 
the  heaviest  downpour  in  the  United  States.  This 
record  was  made  at  Campo  on  August  12,  1891, 
when  16.10  inches  of  rain  fell — 11.50  inches  of  this 
amount  fell  in  eighty  minutes. 

An  important  fact  to  remember  is,  as  General 
Greely  says,  that  "the  region  of  equable  tempera- 
ture covers  less  than  forty  square  miles,"  and  that  in 
equability  the  climate  reaches  its  perfection  within 
the  city  limits  of  San  Diego. 


PLATE  8  OF  THE 

'CLIMATOLOGY  OF 

CALIFORNIA" 

A.  G.  McAoiE 


Precipitation  map  of  California  (after  McAdie),  showing  that 
in  the  vicinity  of  San  Diego  exists  the  region  of  heaviest  rain- 
fall in  southern  California. 


(53) 


CHAPTER  XIII 
THE  LAND-AND-SEA  BREEZE 

IT  appears  to  be  the  universal  testimony  of  per- 
sons who  have  temporarily  been  absent  from 
this  locality  that  their  memory  most  often 
recurs  to  the  winds  of  San  Diego.  This  is  readily 
accounted  for  when  we  find  that  the  average  wind 
velocity  of  San  Diego  is  low  for  a  seacoast  port, 
being  less  than  six  miles  per  hour,  and  that  high 
winds  are  practically  unknown.  These  conditions 
are  brought  about  mainly  by  the  proximity  of  the 
sea  and  desert.  The  latitude  is  such  as  to  remove 
from  all  but  casual  consideration  the  effect  of  the 
northern  storms,  which  generally  enter  the  Pacific 
Coast  about  the  latitude  of  Oregon  and  move  east- 
ward. Unless  the  storm  be  of  unusual  size  or  inten- 
sity, the  wind-system  of  San  Diego  is  not  disturbed. 
The  sea  breeze  is  most  constant,  and  blows  from  the 
northwest  during  all  but  two  months  in  the  year — 
June  and  December — when  the  winds  are  from  the 
southwest  and  northeast.  The  annual  distribution 
of  the  wind  would  give  the  following  percentages 
from  eight  points  of  the  compass :  North  and  north- 
east, 8;  east,  4;  southeast,  3;  south,  7;  southwest,  13; 
west,  22;  and  northwest,  35  per  cent.  In  the  course 
of  the  year  about  50,000  miles  of  wind  traverse  San 
Diego.  May  is  the  month  with  the  greatest  amount 
of  wind,  and  December  records  the  least.  For  over 
twenty  years  recording  instruments  have  traced  on 
paper  every  mile  of  wind  and,  for  every  minute,  the 
direction  of  the  wind.  The  compiled  records  show 

(54) 


The  Land-and-Sea  Breezes  55 

some  interesting  figures.  Before  considering  the 
average  conditions  let  us  examine  the  extremes,  for 
the  unusual  features  in  the  climate  of  any  locality 
are  the  most  convincing.  The  Weather  Bureau 


The  land-breeze.   Ideal  circulation  (water  warmer  than  land) 
3  A.M.  to  9  A.M. 

designates  winds  of  from  o  to  5  miles  an  hour  as 
"calm,"  5  to  15  as  "light,"  15  to  25  as  "moderate," 
25  to  35  as  "brisk,"  35  to  50  as  "high,"  50  to  65  as 
a  gale,  and  from  65  above  as  a  hurricane.  Under 


The  sea-breeze.    Ideal  circulation  (land  wanner  than  water) 
1 1  A.M.  to  6  P.M. 

this  classification  San  Diego  has  a  "brisk"  wind  (25 
to  35  miles  an  hour)  about  three  times  a  year.  Once 
has  the  wind  exceeded  40  miles  an  hour,  and  that 
was  43  on  March  9,  1912.  For  the  past  decade  the 
records  of  the  local  office  of  the  Weather  Bureau 


56       Climate  and  Weather  of  San  Diego 

have  been  used  by  many  foreign  meteorologists  to 
illustrate  the  constancy  of  the  land-and-sea  breeze, 
which  is  caused  by  the  unequal  heating  of  the  land 
and  water.  In  San  Diego  this  breeze  is  said  to 
attain  perfection  in  the  regularity  of  the  change  in 
wind-direction.  Although  nearly  one-half  of  the 
wind  is  from  the  northwest  and  a  point  near  the  west, 
the  land-and-sea  breeze  feature  gives  San  Diego 
some  wind-movement  from  all  directions.  It  must 
be  understood,  however,  that  the  land  breeze  is 
unusually  light,  averaging  less  than  4  miles  an  hour. 
It  blows  from  about  three  until  nine  in  the  morning, 
when  there  is  nearly  a  calm.  The  period  following  the 
land  breeze  lasts  a  couple  of  hours,  and  is  analogous 
to  the  term  "slack-water"  in  the  tides.  The  time  of 
this  calm  period  between  the  land  breeze  and  the 
sea  breeze  changes,  of  course,  with  the  season, 
being  earlier  in  the  summer  and  later  in  the  fall  and 
winter.  In  January  it  covers  nearly  all  the  morning 
hours. 


CHAPTER  XIV 

AVIATION  AND  AIR-MOVEMENT  IN  SAN  DIEGO 


BOUT  ten  or  twelve  years  ago  a  gray  -haired 

ther 


AB 

/"\  gentleman  walked  into  the  Weather  Bureau 
office  and  introduced  himself  as  Octave 
Chanute.  This  was  the  first  visit  of  the  noted  French 
engineer  to  San  Diego.  Led  by  the  attractive  record 
of  San  Diego's  low  wind  velocities  he  came  here  in 
pursuit  of  his  studies  in  aviation.  After  Langley, 
no  scientist  here  or  abroad  contributed  more  to  the 
progress  of  practical  navigation  of  the  air  than  did 
Octave  Chanute.  At  the  time  of  Chanute's  first 
visit  to  San  Diego,  pelicans  were  very  numerous  on 
the  bay,  and,  in  company  with  his  assistants  and 
friends,  he  made  many  instantaneous  photographs 
of  these  interesting  and  picturesque  birds.  He  once 
told  me  that  the  secret  of  air-navigation  lay  in 
imitating  the  flight  of  the  pelican.  Hundreds  of 
photographs  were  taken,  to  be  studied  later  in  his 
Chicago  laboratory.  It  is  said  that  Chanute  started 
the  Wright  brothers  about  this  time  on  their  career 
as  the  first  birdmen.  Unlike  Langley,  Chanute 
lived  to  share  in  the  triumph  of  the  Wrights.  Dur- 
ing the  now  historic  experiments  of  OrviTle  Wright, 
three  years  ago  at  Fort  Myer,  Virginia,  it  was  very 
gratifying  to  be  able  to  renew  acquaintance  with 
Octave  Chanute,  and  to  hear  him  quickly  revert  to 
his  early  experiments  on  San  Diego  Bay.  With 
characteristic  impulsiveness  he  pointed  to  the  soar- 
ing Wright  biplane  as  resembling  his  old  friend,  the 
San  Diego  pelican.  Had  Chanute  lived  to  see 

(57) 


58       Climate  and  Weather  of  San  Diego 

Glenn  Curtiss'  hydro-aeroplane,  first  navigated  in 
San  Diego  air  and  water,  the  similitude  to  the  peli- 
can would  have  been  even  greater. 

SAN  DIEGO'S  LOW  WIND-MOVEMENT 

Glenn  Curtiss  was  likewise  attracted  to  San 
Diego  because  of  the  absence  of  gusty  winds  and  the 
dependability  of  the  air  in  general.  The  United 
States  Military  Aviation  School,  directed  by  Mr. 
Curtiss,  and  located  on  North  Island,  the  low-lying, 
brush-covered  peninsula  across  San  Diego  Bay,  has 
graduated  half  a  hundred  aviators  since  Mr.  Curtiss 
installed  his  school  in  1911.  The  proximity  of  the 
ocean  on  one  side,  and  the  quiet  waters  of  the  bay 
on  the  other,  makes  the  location  ideal  for  both  his 
aeroplanes  and  hydro-aeroplanes. 

TABLE  XII. — Average  Wind  in  Miles  Per  Hour  (1873-1911) 

By  Months 

January 4.9       July 5.8 

February 5.6       August 5.6 

March 6.  i       September 5.6 

April 6.3       October 5.1 

May 6.3       November 5.1 

June 6.0       December 4.9 

Year 5.6 

By  Hours 

1  A.M 3.6         i  P.M 9.6 

2  A.M 3.7  2  P.M 9-9 

3  A.M 3.7  3  P.M 9.7 

4  A.M 3-7  4  P.M 9-0 

5  A.M 3-8  5  P.M 7-9 

6  A.M.. 3.8  6  P.M 6.4 

7  A.M 3.8  7  P.M $.1 

8  A.M 3.9  8  P.M 4.3 

9  A.M 4.5  9  P.M 3.8 

10  A.M 5.9          IO  P.M 3.5 

1 1  A.M ;    7.4          1 1   P.M 3-5 

Noon 8.7      Midnight 3.6 


Aviation  and  Air-Movement  59 

The  records  of  annual  hourly  wind- velocity  show 
that  the  daylight  winds,  that  is  between  seven  in  the 
morning  and  six  at  night,  average  7.2  miles  an  hour. 
Night  winds,  between  seven  at  night  and  six  in  the 
morning,  average  3.8  miles  an  hour.  The  average 
time  of  the  highest  velocity  is  two  o'clock  in  the 
afternoon  when  an  annual  average  of  9.9  miles  is 
recorded.  The  least  wind  is  3.5  miles  an  hour  and 
is  registered  between  ten  and  eleven  at  night.  It  was 
during  that  time  of  the  day  that  the  record  of  amateur 
monoplane  flights  was  madetoTia  Juana,  Mexico,  and 
return,  in  1911.  In  morning  flights  it  is  important 
that  the  course  should  be  over  the  level  country  and 
away  from  debouching  valleys  and  uplifting  head- 
lands. It  is  during  the  first  few  hours  after  sunrise 
that  the  valley  breeze  begins.  This  is  only  the  heavy, 
colder  air  obeying  the  impulse  of  gravity  and  seek- 
ing lower  levels.  The  flow  caused  by  differing  densi- 
ties of  air  may  be  observed  almost  any  morning  over 
the  Bay  of  San  Diego  by  watching  smoke-columns. 
In  a  valley  the  wind  is  stronger  in  the  center  than 
on  either  side,  for  the  same  reason  that  the  current 
in  the  middle  of  a  stream  of  water  is  stronger,  for 
there  it  has  lost  the  friction  of  the  banks.  Knowledge 
of  this  fact  allows  the  aviator  to  fly  up  a  broad 
ravine,  taking  a  central  course.  On  the  way  down, 
however,  the  speed  of  the  aeroplane  must  be  in- 
creased. 

In  a  recently  published  work  on  charts  of  the 
atmosphere,  it  would  appear  that  if  we  are  ever  to 
take  advantage  of  prevailing  air-drifts  from  this 
country  to  Asia,  the  voyage  could  best  be  started 
from  San  Diego.  The  trip  from  Asia  to  America 
would  be  via  a  northern  route. 


CHAPTER  XV 
THE  MIRAGE,  HALO,  AND  AURORA 

AMONG  the  infrequent  meteorological  phenpm- 

/"%    ena  that  have  been  observed  in  San  Diego 

are  mirages,  lunar  and  solar  coronas,  halps, 

and  the  aurora  borealis.    It  is  indicative  of  the  wide 

variety  in  the  climatic  features  of  this  locality  that 

these   optical   and   electric  phenomena,  which   are 

typical  of  the  desert  and  northern  latitudes,  have 

all  been  noted  at  the  San  Diego  Weather  Bureau 

office. 

The  mirage,  that  most  elusive  and  bewildering 
fantasy  of  light  and  air,  can  be  observed  many  times 
a  year  in  San  Diego.  The  common  appearance  of  the 
mirage  in  this  vicinity  is  the  distortion  and  frequent 
inversion  of  distant  objects  over  the  bay  and  ocean. 
The  Coronado  Islands,  for  example,  often  seem  to 
elongate  and  crumple  up,  volcanic  cones  and  spires 
appearing  where  none  exist.  Portions  of  these 
islands  seem  to  dissolve  into  thin  air,  and  sometimes 
they,  as  well  as  ships  appearing  in  the  vicinity,  are 
inverted.  The  mirage  is  simply  a  distorted  or 
shifted,  or  both  distorted  and  shifted,  image  of  real 
objects  that  may  be  observed  through  field-glasses 
of  high  power,  or  even  photographed.  When  the 
weather  conditions  are  favorable,  such  as  during  a 
a  quiet  morning  on  the  bay,  vessels  at  anchor,  or  the 
Coronado  ferry  may  be  seen  apparently  to  leave  the 
water  so  that  the  opposite  shore  may  be  seen  under- 
neath. The  tricks  and  fancies  thus  produced  may 
well  excite  the  credulous.  A  brief  definition  of 

(60) 


The  Mirage,  Halo,  and  Aurora          61 

mirage  is  that  it  is  an  image  produced  by  successive 
bending  of  rays  of  light  passing  through  air-strata 
of  varying  densities. 

CAUSE  OF  SOLAR  AND  LUNAR  HALOS 

Rings  around  the  sun  or  moon,  mock  suns  or 
moons,  are  always  a  source  of  interest  and,  to  some, 
of  needless  apprehension.  We  see  fewer  halos  in  San 
Diego  than  in  colder  or  more  stormy  latitudes.  The 
records  show  that  solar  and  lunar  halos  average  six 
or  seven,  respectively,  in  the  year,  and  that  they 
invariably  occur  from  October  to  April.  The  greatest 
number  of  halos  occurring  in  any  one  year  in  San 
Diego  was  fifty-eight  in  1885.  While  halos  possess 
no  special  significance,  and  are  classed  with  rainbows 
and  other  optical  phenomena,  their  structure  and 
classification  is  not  without  interest  to  a  student  of 
local  climatology.  Two  kinds  of  rings  about  the 
sun  and  moon  are  sometimes  seen  in  San  Diego; 
whether  they  are  halos  or  simple  coronas  depends  on 
the  diameter  of  the  rings.  A  corona  is  always 
observed  when  the  sun  or  moon  is  shining  through 
moderately  thin  clouds,  and  this  circle  has  a  radius 
of  from  4  to  8  degrees,  with  prismatic  colors,  the 
blue  nearest  the  source  of  light.  Halos,  in  their 
commonest  form,  have  a  radius  of  about  22  degrees, 
often  with  brilliant  prismatic  colors,  with  the  red 
nearest  the  sun  or  moon.  Halos  are  caused  by  the 
action  of  sunlight  or  moonlight  on  ice-needles  in  thin 
cirrus  clouds.  In  falling  to  earth  these  minute 
crystals  of  ice  assume  a  horizontal  position,  owing  to 
their  structure  and  rapid  rotation.  The  effect  of 
light  on  these  spiculae  is  to  produce  halos  of  differing 


62       Climate  and  Weather  of  San  Diego 

degrees  of  brilliancy.  When  observed  near  the 
horizon  these  circles  often  intersect  with  secondary 
circles,  and  points  of  intersection  thus  become  very 
bright  and  form  mock  suns  or  mock  moons.  These 
are  sometimes  called  "sun  dogs"  or  "moon  dogs." 
It  is  not  often,  however,  that  the  humidity  above 
San  Diego  is  sufficient  and  well  enough  distributed 
to  produce  such  phenomena. 


THE    AURORA    ;BOREALIS    HAS     BEEN     SEEN    THREE 
TIMES   IN   SAN  DIEGO 

The  aurora  borealis,  "northern  lights,"  or  "merry 
dancers,"  has  been  observed  three  times  in  San 
Diego  in  over  forty  years.  Recent  investigations 
show  that  the  aurora  can  hardly  be  classed  as  a 
meteorological  feature.  It  is  a  manifestation  of 
atmospheric  electricity,  possibly  resulting  from  a 
bombardment  of  the  atmosphere  by  particles  pro- 
jected at  great  velocities  from  the  sun.  The  aurora 
has  been  seen  so  infrequently  as  far  south  as  this 
latitude  that  a  description  of  the  auroras  of  thirty 
years  ago  may  be  interesting.  The  daily  journal  of 
the  Weather  Bureau  of  1882  has  these  entries: 

November  17. — The  first  appearance  of  the  aurora 
was  two  columns,  or  shafts,  of  light  which  shot  up  from 
the  northern  horizon  to  about  20  degrees.  The  completion 
of  the  arch  was  not  visible,  but  the  columns  blended 
together  forming  a  cloud,  or  floating  mass,  of  deep  rose- 
color.  This  varied  in  intensity  until  7.30  p.m.,  when  it 
passed  from  view.  This  is  the  first  aurora  ever  recorded 
in  San  Diego. 

November  19. — Fair  aurora  of  two  luminous  beams 
rising  to  about  20  degrees  and  then  separated.  The  space 


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The  Mirage,  Halo,  and  Aurora          63 

between  the  tops  oj  the  columns  was  of  a  pale  yellow. 
The  phenomenon  lasted  from  4.20  a.m.  until  daylight. 

February  5,  1888. — From  5.10  a.m.  to  5  a.m.  an 
aurora  was  visible  in  the  north  and  west.  The  base  was 
shot  with  green  bands  above  and  rose-color  below.  The 
colors  were  not  very  bright. 

These  three  are  the  only  auroras  ever  witnessed 
in  San  Diego. 


CHAPTER  XVI 

THUNDERSTORMS  AND  OTHER  RARE 
WEATHER  CONDITIONS 

SINCE  the  establishment  of  the  local  Weather 
Bureau  office  in  1871,  San  Diego  has  experi- 
enced sixty-seven  thunderstorms,  thus  aver- 
aging a  little  less  than  two  each  year.  Thunder- 
storms and  attendant  weather  phenomena  have 
always  been  recorded  and  studied  in  detail,  so  that 
each  one  of  these  storms  has  its  own  particular 
history  written  in  the  government  records.  The 
subject  is  an  interesting  one,  both  on  account  of  the 
infrequency  of  these  local  storms  and  the  individual- 
ity of  their  record. 

Thunderstorms,  like  all  other  kinds  of  weather, 
are  caused  by  the  great  aerial  eddies  of  the  atmos- 
phere modified  by  local  conditions.  If  we  examine 
the  daily  weather  map,  we  shall  find  that  thunder- 
storms in  southern  California  generally  occur  in 
the  southwestern  quadrant  of  a  region  of  low 
barometer. 

TABLE  XIII. — Distribution  oj  Thunderstorms  by  Months  and 
Hours.    (Total  number  in  Jorty  years) 


January. 

Day 

Night 
j 

August  . 

Day 

Night 
7 

February 

•a 

4, 

September 

2 

March 

7 

6 

October 

April 

2 

November 

o 

o 

May 

December 

2 

2 

June  

.  .  .  o.  . 

July  

.     .    2     , 

.     c 

Year.  .  . 

...    29.  . 

.     ..    38 

Total. 

.  6- 

7 

"Day"  and  "night"  are  approximately  sunrise  to  sunset  and 
sunset  to  sunrise. 

(64) 


Rare  Weather  Conditions  65 

Distribution  by  Hours  in  the  Twenty-four 

I  A.M 2  I  P.M O 

2A.M I  2  P.M 3 

3  A.M 5  3  P.M 4 

4  A.M 2  4  P.M 2 

5  A.M 2  5  P.M 3 

6  A.M I  6  P.M 2 

7  A.M 2  7  P.M 5 

8  A.M 3  8  P.M 6 

9  A.M 7          9  P.M 4 

10  A.M 5          IO  P.M 2 

1 1  A.M O          II  P.M 4 

Noon o       Midnight 2 

Total 30  Total 37 

These  tables  show  that  thirty-eight  out  of  a 
total  of  sixty-seven  thunderstorms  recorded  in  San 
Diego  in  the  past  forty  years  occurred  during  the 
hours  after  sunset;  more  occurred  in  August  than 
in  any  one  month  of  the  year;  none  have  been 
observed  in  November  and  only  one  in  June.  There 
appear  to  be  two  periods  of  thunderstorm  frequency 
in  the  twenty-four  hours — nine  in  the  morning  and 
eight  in  the  even  ng. 

TWO  WATERSPOUTS  HAVE  BEEN  SEEN   IN  SAN  DIEGO 

As  waterspouts  occur  only  during  thunderstorm 
weather,  they  are  generally  classed  as  attendant 
phenomena.  Two  waterspouts  have  been  observed 
in  San  Diego — the  first  one  on  December  9,  1898, 
and  the  other  on  March  1 1,  1909. 

As  both  of  the  waterspouts  observed  in  San  Diego 
were  similar  in  general  formation,  and  presented  the 
usual  features  common  to  such  phenomena,  they 
will  be  described  together.  A  few  miles  off  Point 
Loma  a  gray  mass  of  nimbus  cloud  overhung  the 
moderate  swell  of  the  sea,  and  from  this  cloud  could 


66       Climate  and  Weather  of  San  Diego 

be  seen  several  convex  projections.  They  would 
extend  downward  as  wisps  of  cloud;  they  would 
withdraw  quickly  until  one  dropped  suddenly  to  the 
sea  and  showed  a  slightly  inclined  column  of  whitish 
vapor.  The  waterspouts  were  1,000  to  1,500  feet 
high,  and  from  100  to  125  feet  in  diameter.  The 
sheath  of  vapor  moved  against  the  wind,  traversing 
the  six  or  eight  miles  of  their  course  in  ten  or  twelve 
minutes.  There  are  evidences  that  the  waterspout 
of  1898  moved  inland  for  a  few  thousand  yards, 
causing  heavy  downpours  which  washed  out  patches 
of  vegetation,  leaving  the  bare  rock  exposed  in  con- 
siderable areas.  The  southern  slope  of  Mount 
Soledad  shows  such  barren  places. 


CHAPTER  XVII 
THE  PHENOMENON  OF  FROST 

THE  month  of  December,  1911,  will  go  down 
in  the  meteorological  history  of  California 
as  one  of  the  frostiest  on  record.  It  was  the 
coldest  but  one  in  the  past  fifty  years  of  temperature 
observations  at  San  Diego.  The  average  daily 
temperature  in  December  was  53  degrees,  and  this 
was  the  lowest  for  the  last  two  decades.  The  num- 
ber of  light  and  heavy  frosts  broke  all  previous 
records.  There  were  no  killing  frosts  in  this  vicinity, 
and  none  have  ever  occurred  in  the  history  of 
San  Diego. 

As  frost  in  San  Diego  is  a  phenomenon,  it  appears 
worth  while  to  consider  its  cause  and  why  this 
region  is  comparatively  free  from  its  injury. 

Horticulturists  have  decided  that  plant-growth 
is  at  a  standstill  when  the  daily  mean  temperature  is 
43  degrees,  or  lower.  Or,  in  other  words,  when  the 
average  twenty-hours'  temperature  is  above  43 
degrees,  plants  are  growing.  Under  this  criterion 
the  mean  daily  temperature  records  of  San  Diego 
show  that  for  forty  years  (or  15,000  days)  there 
were  six  days  when  the  mean  temperature  equalled  or 
dropped  below  43  degrees.  All  of  these  days  occurred 
in  January  of  1880,  1882,  1888,  and  1894.  Putting 
it  in  another  way,  we  may  say  that  since  the  begin- 
ning of  temperature  observations,  which  cover  a 
period  of  15,000  days,  there  were  14,994  days  of 
growing  weather. 

(67) 


68       Climate  and  Weather  oj  San  Diego 

FROST  A  MATTER  OF  AIR-DRAINAGE 

Cold  air  is  denser  than  warm  air,  and  air,  like 
water,  seeks  its  level.  It  is  thus  seen  why  the  tem- 
perature of  low-lying  districts  is  very  much  lower 
than  that  of  the  mesas,  benches,  or  terraces.  Advan- 
tage is  taken  of  this  fact  by  the  orchardists,  who  plant 
lemon  and  orange  trees  on  the  terraces,  while  the 
olive  and  hardier  trees  skirt  the  hillsides.  The  forma- 
tion of  frost  is  thus  seen  to  be  largely  a  matter  of 
air-drainage,  for  frost  usually  forms  first  in  pools 
or  basins. 

WHY  SAN  DIEGO  HAS  NEVER  HAD  A  KILLING  FROST 

In  the  standard  "Climatology  of  the  United 
States,"  issued  by  the  central  office  of  the  United 
States  Weather  Bureau,  appears  this  statement 
on  page  28: 

The  absolute  minimum  temperature  at  San  Diego, 
California,  is  32  degrees,  and  at  Key  West,  Florida,  41 
degrees.  These  are  the  only  Weather  Bureau  stations  in 
the  United  States  where  a  minimum  temperature  below 
freezing  has  not  been  experienced. 

The  reason^why  San  Diego  has  never  experienced 
a  killing  frost  is  because  the  ocean,  over  which  blows 
75  per  cent  of  San  Diego's  winds,  has  a  temperature 
many  degrees  higher  than  the  land.  For  example: 
Shortly  before  sunrise,  at  the  time  of  the  lowest 
temperature  (36  degrees  on  December  26,  1911), 
the  temperature  of  the  ocean  was  59  degrees,  or 
23  degrees  warmer  than  the  land.  The  warm  air 
from  the  ocean  is  transported  over  the  land,  raising 
the  temperature  above  the  danger  point. 


CHAPTER  XVIII 

THE  INTER-RELATION  BETWEEN  OCEAN 
CURRENTS  AND  WEATHER  CONDITIONS 

IT  has  frequently  been  claimed  that  the  Japan 
Current  controls  the  weather  of  the  Pacific 
Coast,  and,  on  the  other  hand,  quite  as  often 
asserted  that  it  has  not  the  slightest  influence  on 
the  climate  of  this  region.  Both  statements  need 
qualification,  for  there  is  a  complex  inter-relation 
between  ocean  currents  and  weather  conditions, 
not  only  on  our  own  Pacific  Coast,  but  everywhere 
all  over  the  earth. 

The  following  brief  account  of  this  inter-relation, 
by  Prof.  W.  J.  Humphreys,  of  the  $  United  States 
Weather  Bureau,  is  offered  as  an  aid  to  a  clearer 
understanding  of  this  much-mooted  subject: 

"There  are  many  things  that  contribute  to  the 
general  circulation  of  the  waters  of  the  earth,  but 
the  principal  cause  of  ocean  currents  is  the  driving 
force  of  the  prevailing  winds  of  the  globe.  Within 
the  tropics,  for  instance,  the  surface  wind  is  usually 
from  the  east,  and  this,  in  the  course  of  many  years, 
has  established  an  equatorial  drift  of  warm  water 
from  east  to  west  across  all  the  great  oceans  of  that 
region.  But  the  drift  is  interrupted  and  deflected  by 
chains  of  islands  and  by  the  coasts  of  continents, 
and  still  further  influenced  in  its  course  by  the  rota- 
tion of  the  earth  which,  in  general,  causes  warm 
currents,  or  those  that  flow  toward  higher  latitudes, 
to  turn  eastward,  and  cold  currents,  or  those  that 
flow  toward  the  equator,  to  turn  westward. 

(69) 


yo       Climate  and  Weather  oj  San  Diego 

"In  this  way  the  equatorial  drift  of  the  Pacific 
Ocean,  that  flows  around  and  among  the  Philippine 
Islands,  merges  into  the  Japan  Current,  which, 
partly  by  the  deflection  of  the  coast  of  China  and 
partly  under  the  influence  of  the  rotation  of  the 
earth,  turns  to  the  northeast,  where  it  is  further 
impelled  along  its  course  by  the  west  winds  of  the 
North  Pacific.  After  crossing  the  ocean  from  west  to 
east,  the  waters  gradually  turn  south,  and  eventually 
merge  with  and  once  more  become  a  part  of  the 
equatorial  drift. 

"In  the  same  way,  the  equatorial  Atlantic  drift 
and  the  Gulf  Stream  are  but  separate  portions  of  a 
continuous  circulation. 

"The  chief  cause,  therefore,  of  the  ocean  currents 
is  persistent  or  prevailing  winds;  but  the  existing 
system  of  currents,  their  number,  location,  and 
direction,  is,  in  great  measure,  determined  by  the 
rotation  of  the  earth  and  by  the  position  and 
extent  of  interfering  and  deflecting  islands  and 
continents. 

"Let  us  see  now  what  effects,  if  any,  ocean  cur- 
rents can  have  upon  the  winds  of  the  globe  that 
keep  them  in  motion,  and  what  modifications  the 
currents  therefore  must  make  of  the  climate  and 
weather  of  the  regions  over  which  these  winds 
themselves  ultimately  pass. 

"It  is  well  known,  and  the  reason  is  obvious,  that 
the  surface  temperature  of  the  ocean  and  the  tem- 
perature of  the  atmosphere  that  for  some  time  has 
been  in  contact  with  it  are  nearly  the  same.  Hence 
any  change  in  the  temperature  of  the  ocean  surface 
changes  approximately  to  the  same  extent  the 
temperature  of  the  winds  that  blow  over  it,  and  thus 


Ocean  Currents  and  Weather  71 

indirectly  the  temperature  of  the  lands  over  which 
they  immediately  pass. 

"In  so  far,  therefore,  as  the  surface  temperature 
of  the  North  Pacific,  for  instance,  is  warmer  because 
of  the  Japan  Current  than  it  would  be  if  no  such  cur- 


Outline  weather  map,  (extended  to  show  weather  conditions) 
at  8  P.M.,  February  i,  1912 

rent  existed,  approximately  to  that  same  extent  are 
the  on-shore  winds  of  Alaska,  British  Columbia, 
and  our  own  west  coast  warmer,  and  also  more 
humid  than  they  would  otherwise  be.  But  just  how 
much  warmer  the  surface  of  the  North  Pacific 
Ocean  is  because  of  the  Japan  Current,  or  the  sur- 
face of  the  North  Atlantic  Ocean  because  of  the  Gulf 


72       Climate  and  Weather  of  San  Diego 

Stream,  no  one  knows  at  all  accurately — it  may  be 
quite  as  much  as  5°  Fahr.  in  each  case.  At  any 
rate,  it  certainly  is  not  negligible  in  amount,  and 
therefore  warm  ocean  currents,  through  the  winds 
they  have  tempered,  undoubtedly  modify  the 
climates  of  certain  favorably  situated  islands  and 
coasts. 

"It  must  not  be  supposed,  however,  that  warm 
and  cold  ocean  currents  are  the  chief  causes  of  the 
climatic  difference  between  Labrador  and  Ireland, 
for  instance,  or  Labrador  and  southern  Alaska,  for 
such  indeed  is  not  the  case.  Here  the  extreme  tem- 
peratures of  Labrador  are  caused  by  the  passage  of 
its  prevailing  wind  over  the  surface  of  a  continent 
which  itself  is  subject  to  wide  temperature  changes, 
while,  on  the  other  hand,  the  equable  climate  of 
Ireland,  say,  is  due  to  the  fact  that  its  prevailing 
winds  come  from  over  the  ocean,  whose  temperature, 
because  of  its  great  heat-capacity  and  mobile  sur- 
face, changes  but  little  from  month  to  month  and 
from  year  to  year.  This  explains  the  chief  cause  of 
the  difference  between  the  two  types  of  climates,  the 
marine  or  equable,  and  the  continental  or  extreme. 
But,  as  already  explained,  the  temperature  of  the 
ocean  surface  itself  is  dependent  in  part  upon  the 
ocean  currents,  and,  therefore,  in  this  way  they 
become  factors  in  the  production  of  the  weather 
and  climate  of  many  places,  though  how  great  their 
influence  it  is  impossible,  as  already  stated,  accu- 
rately to  estimate. 

"In  addition  to  the  above,  there  is  another  and 
even  greater  influence  of  ocean  currents  on  climate 
and  weather,  indirectly  effected  through  the  forma- 
tion and  location  of  permanent  'highs/ 


Ocean  Currents  and  Weather  73 

"By  a  process  perfectly  well  known,  the  explana- 
tion of  which  would  be  out  of  place  here,  because 
necessarily  tedious  and  elaborate,  the  east  winds 
of  the  tropics  and  the  west  winds  of  the  higher 
latitudes  conspire  to  produce  two  belts  of  high  baro- 
metric pressure  practically  parallel  to  the  equator, 
situated  at,  roughly,  30  degrees  north  to  35  degrees 
south,  respectively. 

"If  now  these  belts  were  of  uniform  pressure 
throughout  they  obviously  would  divide  the  earth 
into  three  great  zones,  each  with  its  own  circulation 
and  with  a  radically  altered,  and  probably  much 
reduced,  atmospheric  interchange  the  one  with 
another.  But,  instead  of  being  uniform,  they  have 
sub-permanent  high  centers,  each  of  which  leads  to 
a  vigorous  circulation  from  zone  to  zone  that  pro- 
foundly modifies  the  direction  of  the  prevailing 
winds,  and  hence  the  weather  and  the  climate  in  its 
neighborhood.  And  this  is  of  distinct  importance 
to  San  Diego,  since  one  of  these  centers  lies  just  off 
the  coast  of  southern  California. 

"Now  each  permanent  ocean  'high*  is  at  that 
place  where  a  cold  ocean  current  crosses  a  belt  of 
high  pressure.  It  is  there  because  at  this  place  the 
planetary  winds,  as  above  explained,  and  the  cooling 
effect  of  the  cold  current  both  tend  to  produce  a 
high  barometer,  and  therefore  together  lead  to  a 
greater  pressure  than  either  alone  could  produce, 
or  than  either  alone  at  other  places  actually  does 
produce. 

"The  conclusion,  therefore,  is  that  ocean  cur- 
rents, partly  through  their  influence  on  the  tempera- 
ture and  humidity  of  the  atmosphere,  but  especially 
through  their  influence  in  determining  the  existence 


74       Climate  and  Weather  of  San  Diego 

and  fixing  the  position  of  permanent  ocean  'highs/ 
though  seldom,  if  ever,  the  chief  factor,  do  distinctly 
modify  the  weather  and  the  climate  of  many  parts 
of  the  earth. 

"In  short,  the  entire  circulation  of  the  atmosphere 
and  of  the  ocean  and  the  distribution  of  temperature, 
humidity,  and  rainfall  are  so  intimately  woven 
together  into  one  complex  interdependent  whole 
that  no  change  could  be  made  in  any  one  without 
producing  a  reaction  upon  all  the  others." 


CHAPTER  XIX 
METEOROLOGICAL  MYTHS 

METEOROLOGY  has  the  unusual  distinction 
of  being  the  oldest  as  well  as  the  youngest 
of  the  natural  sciences.  Hieroglyphic  in- 
scriptions record  the  weather  conditions  prevailing 
in  the  valley  of  the  Nile  6,000  years  ago.  These, 
and  succeeding  records,  extending  through  Bible 
times,  and  the  intervening  centuries  up  to  within 
the  past  fifty  years,  were  matters  of  only  individual 
observation.  It  remained  for  the  new  science  of 
meteorology  to  correlate  these  isolated  facts.  With 
the  beginning  of  simultaneous  weather  observations 
in  different  parts  of  the  country  the  new  meteorology 
had  its  birth.  In  the  centuries  that  have  elapsed 
it  is  not  strange  that  changes  in  weather  have  been 
ascribed  to  many  fanciful  sources.  The  variety  of 
meteorological  myths  is  limited  only  by  the  credulity 
of  man. 

San  Diego,  as  a  locality,  is  remarkably  free  from 
many  of  the  popular  misconceptions  of  the  weather 
that  are  still  firmly  believed  in  other  communities. 
The  reason  is  undoubtedly  because  of  the  equability 
of  the  climate  and  the  close  attention  given  weather 
conditions.  The  infrequent  stormy  periods  in  San 
Diego  upset  all  preconceived  notions  as  to  "equinoc- 
tial storms"  and  the  influence  of  the  moon  on  the 
weather.  Even  the  time-honored  almanac,  with  its 
weather-changes  for  every  day  of  the  year,  is 
neglected.  It  is  frequently  remarked:  "I  could  tell 
something  about  the  weather  back  east,  but  out 

(75) 


76       Climate  and  Weather  of  San  Diego 

here  in  California  things  are  different."  Really  the 
only  difference  is  that  in  other  less  regular  climates 
the  changes  are  so  rapid  that  it  is  an  easy  matter  to 
make  almost  any  assumption  fit.  Then,  too,  coinci- 
dences are  remembered,  while  a  large  number  of 
failures  to  coincide  are  forgotten.  The  limitations 
of  this  chapter  make  it  necessary  to  mention  only 
a  few  of  the  more  prevalent  weather  myths,  and  to 
give  some  reasons  why  these  time-honored  beliefs 
should  be  classified  as  superstitions. 

EQUINOCTIAL  STORMS  ARE  UNKNOWN  IN  SAN  DIEGO 
OR   ELSEWHERE 

The  "equinoctial  storm"  is  a  myth  that  is  not 
difficult  to  dispel  in  this  locality;  but,  in  regions 
where  storms  are  frequent,  there  are  generally  a 
sufficient  number  of  disturbances  during  the  latter 
part  of  September  or  March  to  verify  any  prediction, 
provided  always  that  sufficient  leeway  is  given  for 
verification.  The  equinoctial  period  is  only  an  inci- 
dent in  the  annual  history  of  the  earth  when  the 
days  and  nights  are  of  equal  length.  It  has  not  been 
explained  by  the  adherents  of  the  "equinoctial 
storm"  theory  why  wind,  rain,  or  snow  should  more 
frequently  occur  on  the  exact  date  the  sun  crosses 
the  plane  of  the  earth's  equator  than  during  other 
days  of  those  months.  A  rigid  examination  of 
weather  records  at  San  Diego  and  other  stations 
proves  that  storms  do  not  occur  more  frequently 
on  the  2ist  of  September  or  the  2ist  of  March  than 
on  other  arbitrary  dates. 


Meteorological  Myths  77 

THE  MOON   DOES   NOT   INFLUENCE  THE  WEATHER 

The  moon  does  not  influence  the  weather,  but  it 
does  indirectly  lengthen  the  day.  The  influence  of 
the  tides  retards  the  earth's  rotary  motion  which 
causes  it  to  slow  up  very  gradually;  in  fact  the  day 
is  lengthened  one-quarter  of  a  second  in  3,600  years. 
Many  persons  give  credence  to  the  control  of  the 
weather  by  the  moon,  but  examination  of  the  reason 
for  their  faith  does  not  disclose  any  scientific  founda- 
tion. The  astronomer  Herschel  was  the  last  scientist 
of  repute  to  father  lunar  control  of  the  earth's 
weather;  but  his  theory  was  abandoned  after  a  study 
of  weather  statistics  during  different  phases  of  the 
moon.  Out  of  the  innumerable  combinations  in 
which  the  moon  figures  there  is  space  to  consider 
but  one:  "If  the  points  of  the  new  moon  are  turned 
up,  the  weather  will  be  dry;  if  turned  down,  it  will 
be  wet."  Another  version  of  the  proverb  is  that  it 
will  be  dry  if  the  upturned  points  allow  the  legendary 
Indian  to  hang  up  his  powder  horn.  Is  it  not  strange, 
even  in  the  absence  of  data  to  verify  either  one  or 
the  other  of  these  contradictory  statements,  that 
this  superstition  should  linger,  when  a  little  reason- 
ing would  show  that  such  an  aspect  of  the  moon 
would  be  the  same  for  all  places  on  the  same  circle 
of  latitude?  If  the  inclination  of  the  horns  of  the 
moon  affected  the  weather,  then  the  weather  would 
be  the  same,  for  example,  from  southern  California 
to  South  Carolina.  We  know  that  this  is  not  the 
case,  for,  following  San  Diego's  32-degree  belt  east- 
ward to  Charleston,  widely  diverse  climates  are 
encountered.  We  have  the  dry  climate  of  the 
elevated  plateaus  of  Arizona  and  New  Mexico  and  the 


78       Climate  and  Weather  of  San  Diego 

plains  of  Texas,  the  changeable  weather  of  Okla- 
homa, the  frequent  storms  of  Louisiana,  Arkansas, 
Mississippi,  and  Alabama,  and  the  south  Atlantic 
rains  of  the  coasts  of  Georgia  and  South  Carolina. 
The  old  adage  says: 

The  moon  and  the  weather 
May  change  together, 
But  change  oj  the  moon 
Does  not  change  the  weather. 

Nothing  is  so  mechanical  as  the  moon,  nothing  is 
so  uncertain  as  the  weather,  and  yet  the  myth  of 
lunar  control  of  weather  conditions  has  persisted 
for  centuries,  and  will  doubtless  be  credited  in  cen- 
turies to  come.  The  explanation  is  a  working  out 
of  a  psychological  instead  of  a  physical  law.  Did  not 
Fisher  explain  it  when  he  said : 

There  is  no  consciousness ,  on  the  part  oj  those  from 
whom  the  myth  emanates,  that  this  product  of  their  fancy 
and  feeling  is  fictitious.  From  the  myth  the  element  of 
deliberation  is  utterly  absent.  There  is  no  questioning 
of  its  reality,  no  criticism  or  inquiry  on  the  point,  but 
the  most  simple  unreasoning  faith." 


ALMANAC  WEATHER  PREDICTIONS  HAVE  BEEN 
UNCHANGED  FOR  A  CENTURY 

History  records  that  the  almanac's  so-called 
daily  weather  predictions  for  years  in  advance  had 
its  origin  among  the  Greeks,  and  in  this  manner: 
For  popular  use  they  posted  daily  weather  conditions 
as  they  occurred;  wind,  rain,  and  cloud  were  care- 
fully noted,  and  later  they  added  the  rising  and 
setting  of  the  stars  to  indicate  time.  Consequently, 


Meteorological  Myths  79 

the  weather  and  stars  were  afterwards  erroneously 
associated  together.  We  have  in  San  Diego  a  local 
parallel  of  the  publication  in  the  daily  newspapers 
of  the  weather  report  in  the  same  column  with  the 
tide  table,  leading  many  persons  to  believe  that 
from  this  simple  accident  of  proximity  there  is  a 
relationship  between  them.  In  the  days  of  Greece 
an  endeavor  was  made  to  correct  the  association 
of  the  accurate  almanac  record  of  the  stars  with  the 
weather  conditions,  but  the  superstition  steadily 
gained  in  popularity  until  it  became  an  accepted 
fact.  According  to  Hellmann,  one  of  the  ancient 
warnings  was  uttered  by  Gemenius  two  thousand 
years  ago: 

Concerning  the  teachings  of  weather  phenomena, 
there  is  a  prevalent  and  erroneous  superstition  that  atmos- 
pheric phenomena  depend  on  the  rising  and  setting  of  the 
stars.  Mathematics  and  natural  history  teach  a  totally 
different  conception. 

The  attractive  myth  grew,  however,  until  it 
became  incorporated  into  the  life  of  the  people. 
This  superstition  is  prevalent  even  today  in  many 
parts  of  the  country,  and  the  fiction  of  the  weather 
is  accepted  with  the  facts  of  the  astronomical  infor- 
mation. Time  has  not  changed  the  character  or 
the  scope  of  these  so-called  weather  predictions. 
The  author  has  a  collection  of  original  Farmer's 
Almanacs  published  in  Boston  a  century  ago,  and 
it  is  interesting  to  note  in  comparison  with  the 
latest  patent  -  medicine  almanac  that  the  so-called 
predictions  and  their  phraseology  are  identical. 


CHAPTER  XX 
MARINE  METEOROLOGY  IN  SAN  DIEGO 

THE  first  person  to  make  meteorological  obser- 
vations in  the  vicinity  of  San  Diego  was 
Captain  Juan  Rodriguez  Cabrillo,  when, 
with  his  frail  caravels,  the  "San  Salvador"  and 
"Victoria,"  in  September,  1542,  he  entered  the  Bay 
of  San  Diego.  Maps  and  instruments  were  very 
crude  370  years  ago,  and  navigation  had  none  of  the 
safeguards  that  science  has  since  given  it.  The  sea 
was  then  a  trackless  waste,  abounding  in  hidden 
perils  of  unknown  currents  and  winds.  History  does 
not  show  much  advance  in  the  science  of  marine 
meteorology  until  the  last  fifty  years.  Benjamin 
Franklin,  on  his  homeward  voyage  from  England 
in  1739,  kept  records  of  the  weather  and  water 
temperatures,  using  an  English  Fahrenheit  ther- 
mometer, and  suggested  a  method  of  determining 
the  approach  of  vessels  to  the  American  coast  by 
the  temperature  of  the  water.  Thus  the  brilliant 
Franklin  was  the  first  American  to  make  sugges- 
tions as  to  the  utility  of  marine  meteorological 
observations. 

It  remained  for  another  American,  Lieut.  M. 
F.  Maury,  author  of  that  picturesque  and  highly 
interesting  "Physical  Geography  of  the  Sea,"  to  be 
the  first  to  interest  a  nation  in  the  publication  of 
sailing  charts  based  on  the  data  collected  from 
ships'  logs.  Until  the  beginning  of  the  Civil  War 
terminated  his  career  as  a  United  States  naval 
officer,  Maury  was  successful  as  a  hydrographer, 

(80) 


Marine  Meteorology  in  San  Diego       Si 

founding  that  Bureau  of  the  Navy.  The  Navy 
collected  the  data  and  published  meteorological 
charts  until  about  six  years  ago,  when  an  exchange 
of  duties  was  arranged  between  the  Navy  and  the 
Weather  Bureau.  The  latter  turned  over  to  the 
Navy  its  system  of  wireless  telegraphy  in  exchange 
for  the  marine  meteorological  work.  Rear  Admiral 
H.  N.  Manney,  U.S.N.,  retired,  now  a  resident 
of  San  Diego,  was  a  member  of  the  presidential 
committee  that  arranged  the  exchange. 

SAN  DIEGO   IS  ONE  OF  THE   EIGHTEEN   MARINE 
CENTERS   IN  THE   UNITED   STATES 

There  are  eighteen  stations  of  the  Weather 
Bureau  designated  as  "Marine  Centers'*  where 
ocean  reports  are  collected,  compiled,  and  after- 
wards forwarded  to  the  central  office  of  the  Weather 
Bureau  at  Washington.  San  Diego  was  among  the 
first  of  such  stations  to  be  established.  A  majority 
of  all  the  vessels  sailing  the  seas  take  a  simultaneous 
observation  of  meteorological  instruments  at  Green- 
wich noon,  and  it  is  entered  on  special  forms  fur- 
nished by  the  United  States  Weather  Bureau.  Sup- 
plementing this  noon  observation,  readings  of  the 
barometer  and  thermometer  are  made  hourly  by 
all  the  war  vessels  of  the  different  countries,  and  the 
merchant  ships  make  a  record  of  such  conditions 
every  four  hours.  The  Weather  Bureau  has,  in  all, 
about  3,000  observers  of  every  nationality,  and  from 
these  reports  prepares  daily  synoptic  charts  of 
meteorological  data,  thus  being  enabled  to  plot 
the  weather  conditions  prevailing  over  the  oceans 
from  day  to  day  for  the  purpose  of  tracing  storm- 


82       Climate  and  Weather  of  San  Diego 

tracks,  percentages  of  fog,  prevailing  direction  of 
wind,  trade-wind  limits,  pressure,  and  temperature. 


WORLD   METEOROLOGY   ADVANCING   BY 
COOPERATION   OF   SHIPMASTERS 

Mariners  who  cooperate  in  this  work  are  serving 
their  own  interests,  as  the  compiled  results  of  their 
observations  are  returned  to  them  free  of  cost  on  the 
meteorological  charts.  In  the  early  days  of  marine 
meteorology,  much  of  the  data  was  buried  in  official 
files;  but  now,  under  modern  office  methods,  every 
item  of  accurate  information  is  used.  The  result 
of  this  work  is  greater  safety  on  the  seas,  increased 
efficiency  in  navigation,  and  economy  of  time  and 
power.  By  charting  great-circle  sailing  routes,  so 
as  to  take  advantage  of  favoring  winds,  time  is 
saved  in  sailing  vessels  and  fuel  in  steamships. 
These  are  some  of  the  practical  gains  to  commerce. 
The  impetus  given  to  meteorology  by  enlisting  the 
services  of  shipmasters  throughout  the  world  con- 
siderably advances  this  science.  While  the  deduc- 
tions made  from  marine  meteorological  observa- 
tions have  frequently  been  of  a  negative  nature, 
such  work  has,  nevertheless,  laid  the  foundation 
for  a  future  treatment  of  the  meteorology  of  the 
earth  as  a  whole  that  will  be  both  consistent  and 
comprehensive. 


CHAPTER  XXI 

FORECASTING  SAN  DIEGO  WEATHER 

FEBRUARY  and  March  of  1912  in  San  Diego 
were  remarkable  months  as  regards  deficient 
and  excessive  rainfall.  In  the  former  no  rain 
fell,  and  in  the  latter  there  were  more  rainy  days 
than  ever  before  experienced  in  any  month  since 
the  record  began.  Notwithstanding  the  phe- 
nomenally large  number  of  rainy  days  in  March, 
the  Weather  Bureau  correctly  forecast  the  twenty 
rainy  days  as  well  as  the  eleven  fair  days.  In  con- 
sidering the  actual  atmospheric  conditions  which 
then  prevailed,  a  study  of  the^  conditions  during 
these  record-breaking  months,  including  both  fair 
and  stormy  weather,  can  be  gained  only  by  examin- 
ing the  weather  map.  Until  the  weather  map  was 
introduced  (which  was  less  than  a  generation  ago), 
correct  weather  forecasts  were  impossible.  The 
weather  map  is  practically  an  instantaneous  photo- 
graph of  the  state  of  the  weather  at  the  hours  of 
observation. 

HOW  THE   WEATHER   MAP   IS   MADE 

Scattered  over  the  United  States  are  some  200 
weather  stations  which  send  simultaneous  observa- 
tions of  barometric  pressure,  temperature,  rainfall, 
wind  direction  and  velocity.  These  observations 
are  made  at  8  A.M.  and  8  P.M.  75th  meridian  time,  or 
5  A.M.  and  5  P.M.  Pacific  time.  The  system  of  obser- 
vation and  transmission  has  been  so  perfected  that 

(83) 


84       Climate  and  Weather  of  San  Diego 

within  thirty  minutes  complete  returns  from  all 
portions  of  the  United  States  have  been  received 
in  Washington  and  exchanges  made  in  all  of  the 
larger  cities.  The  San  Diego  station  receives  both 
morning  and  evening  reports,  but  the  morning  map 
only  is  published  and  used  in  forecasting.  As 
rapidly  as  the  reports,  which  are  in  cipher,  are 
received,  they  are  translated  and  entered  on  the 
map.  Lines  are  drawn  connecting  regions  of  equal 
barometric  pressure,  the  wind  is  indicated  by  arrows, 
the  character  of  the  weather  (fair,  cloudy,  etc.) 
is  shown  by  symbols,  the  rain  by  shaded  portions  and 
the  temperatures  by  dotted  lines.  The  result  gives 
a  map  like  the  specimen  shown  in  the  accompany- 
ing illustration. 

THE    PASSAGE    OF    "HIGHS"    AND    "LOWS"    CONTROLS 
WEATHER   CONDITIONS 

The  words  "high"  and  "low"  refer1  to  the  barome- 
ter and  indicate  that  it  is  relatively  high  or  low. 
Pressure  in  this  instance  is  not  force-^-a  high  pres- 
sure area,  for  example,  is  simply  a  region  which  has 
a  higher  barometric  value  than  the  surrounding 
region.  Both  of  these  eddies  move  along  with  the 
general  drift  of  the  air,  but  the  movement  within 
these  eddies  has  a  spiral  tendency.  The  wind  is 
outward  and  downward  in  a  "high,"  and  inward 
and  upward  in  a  "low."  The  weather,  during  the 
winter,  is  dry  and  cool  when  a  "high"  area  controls, 
and  relatively  moist  and  warm  when  a  "low"  area 
prevails,  but,  so  far  as  temperature  is  concerned, 
generally  the  reverse  during  summer.  Another 
interesting  feature  of  these  barometric  pressure 


Forecasting  San  Diego  Weather          85 

areas  is  that,  owing  to  their  circular  character, 
stations  hundreds  of  miles  to  the  east  of  San  Diego 
are  invaluable  for  forecasting.  Owing  to  the  round 
or  oval  shape  of  barometric  areas,  reports  from 


Fair-weather  type  Rain  type 

Actual  weather  maps  of  8  A.M.,  February  15,  1912,  and  8  A.M., 
March  i,  1912.  Atmospheric  pressure  in  inches.  Wind  direction 
shown  by  arrows. 

Winnemucca,  Nevada,  and  Flagstaff,  Arizona,  fre- 
quently show  the  shape  and  depth  of  a  depression 
whose  southwestern  limits  are  hundreds  of  miles  at 
sea  off  the  coast  of  southern  California. 

The  map  of  February  15,  1912,  is  a  type  common 
to  fair  weather  for  the  reason  that  the  high  area 
prevails  more  than  two-thirds  of  the  time.  In  this 


86       Climate  and  Weather  oj  San  Diego 

chart  the  wind  will  be  noted  as  blowing  outward 
from  the  center  of  the  high,  and  that  to  the  south- 
ward the  skies  are  clear  and  there  is  absence  of  rain. 
On  the  contrary,  the  map  of  March  i  is  distinctly 
a  rain  type.  Warm  and  humid  winds  are  blowing 
into  the  center  of  the  low  area,  and  the  high  area 
to  the  eastward  Slocks  the  further  drift  of  the  low. 

Rainfall  is  the  most  difficult  weather  feature  to 
predict;  wind  is  readily  forecast,  for,  after  locating 
the  low  and  high  areas,  the  direction  and  velocity 
of  the  wind  cease  to  be  matters  of  conjecture.  The 
winds  in  a  low  area  always  blow  spirally  in  a  direc- 
tion opposite  to  the  hands  of  a  watch;  in  a  high  area 
spirally  outward  in  the  opposite  direction.  The 
velocity  of  the  wind  depends  on  the  barometric 
gradient — that  is,  if  the  lines  of  barometric  pres- 
sure are  close  together  on  the  map,  the  winds  will 
be  proportionately  brisk.  Temperature  changes  are 
predicted  by  remembering  that  the  wind  preceding 
and  attending  a  "low"  is  warm,  and  in  a  "high," 
cool. 

Weather  forecasting  would  be  comparatively 
easy  if  these  whirling  air-masses  'traveled  across  the 
country  at  a  regular  rate,  but  often  they  have  a 
disconcerting  way  of  stopping  en  route  on  their 
eastern  journey.  Sometimes  the  procession  of  high 
and  low  areas  will  move  in  an  orderly  manner  like 
beads  on  a  string,  but  more  frequently  a  well- 
defined  area  will  dissipate  in  the  upper  air  levels  or  an 
insignificent  low  area  will  deepen  and  spread  out  until 
it  covers  the  greater  part  of  the  United  States. 

These  explanations  will  show  why  the  Weather 
Bureau  makes  no  attempt  to  forecast  the  weather 
from  local  conditions  at  any  particular  station,  and 


Forecasting  San  Diego  Weather          87 

that  it  bases  its  forecasts  upon  the  weather  prevail- 
ing over  a  large  extent  of  territory  as  shown  by  the 
regular  telegraphic  reports.  The  forecasters  of  the 
Weather  Bureau  have  no  secrets,  for  they  share 
the  results  of  their  study  and  investigations  with  a 
generally  interested  public. 


CHAPTER  XXII 
LOCAL  WEATHER  SIGNS 

SAN  DIEGO  is  an  ideal  place  to  study  meteorol- 
ogy— even  without  instruments.  The  sea,  the 
mountains,  the  plateaus  and  the  desert  are 
within  reach  of  the  vision,  and  the  effect  of  the 
ocean  of  air  over  these  physical  configurations  of 
the  earth  can  be  studied  hourly  and  daily,  and  from 
month  to  month,  producing  a  moving  picture  of 
atmospheric  conditions  that  will  interest  all  who 
pause  and  study  it.  We  have  only  to  lift  our  eyes 
to  see  the  glory  and  majesty  of  nature  displayed 
in  this  region  with  a  lavish  variety. 

While  instruments  and  instructions  are  neces- 
sary for  accurate  results,  the  science  of  meteorology 
can  be  studied  to  a  certain  extent  without  books 
or  instruments,  the  only  requisites  being  an  accurate 
eye,  a  quick  ear,  and  clear  discernment  between 
cause  and  effect.  Nature  yields  her  secrets  most 
readily  to  the  patient  and  painstaking  observer. 

FORETELLING  THE  WEATHER  WITHOUT  INSTRUMENTS 

Every  region  has  its  local  weather  signs  from 
which  much  can  be  learned  by  watching  the  sky 
as  to  existing  and  approaching  meteorological 
changes.  All  weather  conditions  concern  the  air, 
and  these  may  be  divided  into  five  classes:  Those 
relating  to  the  temperature  of  the  air  as  felt  by  the 
human  body;  the  movement  of  the  air  which  includes 
the  varying  wind  direction  and  velocity;  the  moist- 

(88) 


Local  Weather  Signs  89 

ure  in  the  air,  as  exhibited  by  clouds;  rings  around 
the  sun  and  moon;  falling  smoke  and  kindred  phe- 
nomena, and  the  homogeneity  of  the  air,  wnich 
allows  clear  vision  and  good  hearing. 

CLOUDS  ARE  THE  BEST  GUIDES  OF  LOCAL  WEATHER 
CHANGES 

Of  all  natural  phenomena  the  clouds  are  the 
best  indicators  of  the  weather.  Observations  of 
their  structure,  height,  and  direction  are  excellent 
guides  to  weather  changes.  In  San  Diego  it  is 
sometimes  difficult  for  the  beginner  to  determine 
whether  the  clouds  are  of  the  rain-making  or  of 
the  sun-shade  variety:  if  the  cloud  is  not  well 
defined  and  the  islands  and  mountains  can  be  seen 
underneath,  then  the  veto  cloud  is  in  evidence  and 
it  may  be  expected  to  dissipate  in  the  morning.  If 
above  the  lower  cloud  are  seen  glimpses  of  an 
upper  and  lighter  covering,  then  the  sky  is  threat- 
ening and  especially  so  if  the  upper  clouds  have 
a  southerly  direction.  Experience  shows  that  the 
direction  of  the  upper  clouds  eventually  becomes 
that  of  the  surface  wind  direction.  It  is  an  indi- 
cation of  rain  if  the  wisps,  tips,  and  ragged  edges 
of  the  clouds  trend  upwards  and  incline  from  south 
to  north,  for  they  thus  mark  the  ascending  air 
movement  which  always  precedes  rain.  If  the  clouds 
change  from  a  lower  to  a  higher  ievel,  fair  weather 
is  assured. 

A  cloud-cap  over  Otay  mountain  or  San  Miguel 
peak  is  a  precursor  of  rain.  Clouds  of  great  height 
are  disclosed  by  the  mistiness  of  the  stars  and  rings 
about  the  sun  or  moon.  The  proverb 


90       Climate  and  Weather  of  San  Diego 

Rainbow  in  morning,  sailors  take  warning; 
Rainbow  at  night,  sailors'  delight 

is  true  because  the  rainbow  in  the  morning  is  in  the 
western  sky,  from  which  direction  storms  normally 
move.  In  the  evening  the  rainbow  is  in  the  east,  as 
evidence  that  the  rainstorm  has  passed  the  observer. 

SAID   PRAYERS    FOR   RAIN    ONLY   WHEN    SOUTH   WIND 
PREVAILED 

It  was  San  Diego's  best-loved  priest,  the  late 
Father  Ubach,  who  refused  to  offer  prayers  for  rain 
unless  the  wind  stayed  in  the  south  for  three  days. 
The  good  father  was  a  keen  student  of  the  weather, 
as  frequent  conversations  with  him  attested.  Winds 
precede  rain  when  they  blow  either  steadily  from 
the  south,  or  in  gusts  from  the  east.  Northerly 
progression  of  wave-crests  is  another  manifestation 
of  coming  storms,  as  are  also  wild  ducks  and  geese 
flying  south  after  the  first  northern  storm.  Wild 
birds  always  use  the  storm  winds  and  are  borne  at 
great  speed  to  the  south  by  taking  advantage  of  the 
spiral  winds  in  a  storm  center. 

WHY    INCREASED    AUDIBILITY    AND    VISIBILITY    ARE 
PROGNOSTICS   OF   RAIN 

A  San  Diego  physician  says  that  he  can  always 
foretell  rain  when  he  hears  the  rumble  of  the  Santa 
Fe  trains  at  night,  or  sees  the  canons  on  the  Coro- 
nado  islands  by  day.  This  is  true,  for  local  rainstorms 
are  frequently  preceded  by  increased  audibility 
of  sounds  at  night,  such  as  the  rumble  of  trains, 
whistling  buoys,  church  bells,  etc.,  and  in  the  day- 


Local  Weather  Signs  91 

time  distinct  objects  appear  much  nearer  because 
the  air  then  has  a  uniform  distribution  of  tempera- 
ture and  moisture.  Normal  air  at  sea-level  is  a 
mixture  of  warm  and  cold  currents  of  varying 
humidities,  which,  through  irregular  refraction  and 
reflection,  obstruct  to  a  considerable  degree  both 
light  and  sound. 


CHAPTER  XXIII 

METEOROLOGICAL    INSTRUMENTS 

IT  is  not  generally  known  that  one  of  the  most 
valuable  weather-recording  appliances  now  in 
use  by  most  meteorological  observatories  of  the 
world  was  invented  by  an  army  officer  while  on  the 
San  Diego- Yuma  stage-coach  forty  years  ago.  While 
disposing  of  obsolete  instruments  in  1896,  the 
writer  found  an  old  wind -register  bearing  a  plate 
engraved  "Anemograph  No.  13,  Invented  by 
Lieutenant  Gibbon,  U.  S.  A."  The  plate  was 
removed  and  sent  as  a  souvenir  to  Major  Gibbon, 
then  living  in  Washington.  In  his  acknowledge- 
ment he  gave  the  interesting  information  that  he 
invented  the  anemograph  in  the  early  seventies, 
while  taking  the  tedious  stage  ride  from  San  Diego 
to  Yuma.  Thus  San  Diego  is  closely  associated  with 
the  first  automatic  wind-register.  The  Gibbon 
anemograph  has  since  been  superseded  by  more 
intricate  automatic  instruments,  but  the  principle 
of  the  early  pattern,  consisting  of  a  drum  on  a  spiral 
shaft  actuated  by  clockwork,  remains  unchanged, 
and  has  been  a  unique  feature  in  this  model  of 
chronograph.  The  local  station  of  the  United  States 
Weather  Bureau  has,  from  its  establishment,  been 
an  early  recipient  of  the  most  approved  meteorologi- 
cal instruments,  as  they  were  issued  from  WasTi- 
ington.  Continuous  automatic  registration  is  main- 
tained of  atmospheric  pressure,  temperature,  humid- 
ity, wind  velocity  and  direction,  sunshine,  and  rain. 
Some  idea  of  the  weather-recording  equipment  may 

(92) 


Meteorological  Instruments  93 

be  gained  from  the  photograph  facing  page  63 
which  shows  the  apparatus  in  use  at  the  local 
Weather  Bureau  station. 

The  most  valuable  instrument  to  meteorologists 
is  the  barometer,  which  measures  the  pressure  of 
the  air.  There  are  two  kinds  of  barometers,  mer- 
curial and  aneroid,  and  both  are  used  at  the  local 
station.  The  mercurial  barometer  is  simply  a  glass 
tube  sealed  at  one  end  and  filled  with  mercury. 
The  height  of  the  mercury  in  the  tube  shows  the 
weight  of  the  air,  so  when  we  speak  of  the  barometer 
reading  29.98  inches  it  is  meant  that  the  weight  of 
the  atmosphere  is  balanced  by  29.98  inches  of  mer- 
cury. The  aneroid  barometer  is  used  in  the  form  of 
a  barograph.  The  changing  air-pressure  contracts 
and  expands  a  series  of  corrugated  vacuum  boxes 
and  the  motion  is  shown  by  means  of  a  recording 
pen  that  traces  the  line  on  a  revolving  cylinder. 

THERMOMETER  LOCATED  AT  SAN  DIEGO  MISSION 
IN    1840 

The  temperature  of  the  air  is  measured  by  several 
kinds  of  thermometers — mercurial,  alcohol,  and 
electric.  Observations  with  mercurial  thermometers 
were  begun  in  San  Diego  in  1849  and  continued 
without  interruption  to  the  present  day.  In  1872 
an  alcohol  minimum  thermometer  (showing  the 
lowest  point  reached)  was  installed  in  San  Diego, 
together  with  a  maximum  thermometer  which  by 
means  of  a  constriction  near  the  bulb  shows  the 
highest  point  registered  by  the  mercury.  In  1892 
continuous  automatic  records  of  temperature  were 
begun  by  using  a  thermograph,  which  traces  a  line 


94       Climate  and  Weather  of  San  Diego 

on  a  cylinder  turned  by  clockwork.  All  the  ther- 
mometers are  exposed  on  the  roof  some  distance 
from  the  office  rooms,  and  to  enable  the  observer 
to  answer  inquiries  more  readily,  an  electric-tele- 
thermpscope  was  installed  about  three  years  ago. 
This  instrument  gives  the  temperature  at  a  dis- 
tance by  means  of  electrical  resistance  coils  and  a 
galvanometer.  Although  there  are  seven  varieties 
of  thermometers  in  use,  there  is  less  than  a  degree's 
variation  between  them. 


HOW  HUMIDITY  IS  MEASURED 

The  humidity  of  the  air  was  observed  in  1871  by 
using  two  thermometers  placed  side  by  side,  one 
with  a  bit  of  moistened  wicking  around  the  bulb. 
By  means  of  tables,  prepared  from  actual  observa- 
tions in  the  laboratory,  the  difference  in  tempera- 
ture between  the  two  thermometers  showed  the 
amount  of  moisture  in  the  air.  Eighteen  years  later 
an  improved  humidity  apparatus  called  the  whirled 
psychrometer  was  installed.  By  means  of  gears  the 
thermometers  were  rapidly  whirled,  thus  securing 
satisfactory  ventilation.  Since  1908  the  humidity 
has  been  continuously  recorded  by  means  of  a  hair 
hygrograph.  When  the  hair  is  damp  it  absorbs  more 
moisture  and  increases  in  length;  when  the  air 
becomes  drier  the  moisture  evaporates  and  the  hair 
shortens.  These  variations  in  humidity  are  traced 
on  a  revolving  cylinder  similar  to  a  thermograph. 
Since  the  installation  of  the  hygrograph,  a  range  in 
relative  humidity  from  2  to  100  per  cent  has  been 
recorded,  or  from  nearly  absolute  dryness  to  com- 
plete saturation  of  the  air. 


Meteorological  Instruments  95 

THE  SUN  MAKES   ITS  OWN   RECORD 

A  small  brass  camera  traced  the  sunshine  on  a 
piece  of  blue-print  paper  from  1880  until  1897, 
when  an  electric  sunshine  recorder  was  installed. 
This  device  constitutes  an  air,  alcohol  and  mercurial 
thermometer  in  a  vacuum  tube,  where  two  platinum 
wires  are  inserted.  When  the  sun  shines  on  the 
blackened  thermometer  bulb  the  air  expands  (the 
absorption  is  greater,  thus  increasing  the  expansion), 
forcing  the  mercury  up  to,  and  in  contact  with  the 
platinum  points.  This  completes  the  circuit  and 
actuates  an  electrical  marker  in  the  office.  ^  The 
apparatus  is  so  delicate  that  a  passing  cloud  inter- 
cepting the  sunlight  for  only  a  minute  will  be  shown 
on  the  record  sheet.  During  the  solar  eclipse  of 
1911,  this  recorder  showed  its  exact  duration  in 
minutes. 

The  pattern  of  the  rain-gage  is  so  simple  that  it 
is  very  much  doubted  if  its  principle  has  materially 
changed  since  the  first  one  was  set  up  in  the  old 
San  Diego  churchyard,  sixty  years  ago.  A  rain-gage 
consists  of  a  brass  funnel  eight  inches  in  diameter 
with  a  two-inch  flange.  The  rain  falling  into  this 
funnel  passes  into  a  tube  2.56  inches  in  diameter 
which  therefore  has  an  area  one-tenth  that  of  the 
funnel.  To  measure  the  rain,  a  small,  thin  cedar 
stick  marked  off  in  tenths  of  inches  is  dropped  into 
the  tube,  and  the  depth  to  which  the  stick  is  moist- 
ened shows  the  rain  in  inches  and  hundredths.  A 
simple  recording  float  rain-gage  was  installed  in 
San  Diego  in  1891,  but  this  was  replaced  by  the 
present  style  of  tipping  bucket  in  1898.  The  tipping 
bucket  is  a  small  and  perfectly  balanced  receptacle 


96       Climate  and  Weather  of  San  Diego 

divided  into  two  compartments,  each  holding  one- 
hundredth  of  an  inch  of  rain.  When  one  side  of  the 
bucket  fills  it  overbalances  and  completes  an  elec- 
tric circuit  recording  the  amount  on  a  register  in  the 
office. 

An  anemometer  consisting  of  four  hollow  hemis- 
pheric metallic  cups  revolving  on  a  vertical  axis  has 
recorded  every  mile  of  wind  in  San  Diego  since 
1871.  The  cups  of  the  anemometer  approximate 
500  revolutions  to  the  mile  of  wind. 

The  direction  of  the  wind  has  been  traced  each 
minute  by  means  of  a  delicately  balanced  wind- 
vane  for  nearly  twenty  years.  The  changes  in  the 
direction  of  the  wind,  every  mile  of  wind  movement, 
every  hundredth  of  an  inch  of  rain,  and  every  min- 
ute of  sunshine  are  automatically  inscribed  in  the 
office  on  an  instrument  called  the  metrograph. 
This  is  the  latest  improvement  of  the  original 
Gibbon  wind  -  register.  All  of  these  important 
atmospheric  elements  are  accurately  traced  in  dif- 
ferent-colored inks  at  the  exact  time  of  their  occur- 
rence. The  wind,  rain,  and  sunshine  are  marked  in 
parallel  columns  so  that  even  a  beginner  may  see  in 
a  graphic  manner  the  relationship  between  these 
elements.  The  rainfall  is  registered  by  indentations, 
wind  direction  is  dotted,  wind  velocity  is  shown  by 
offset  marks,  and  the  sunshine  is  clicked  off  in  regular 
"upstairs  and  downstairs"  tracings. 


CHAPTER  XXIV 

THE  WEATHER  KIOSK  IN  THE  PLAZA 

WHEN  in  the  city  of  Washington  a  few  sum- 
mers ago,  the  writer  noticed  what  appeared 
to  be  a  miniature  Greek  temple  on  the 
spacious  grounds  of  the  United  States  Weather 
Bureau.  On  inquiry  it  was  found  to  be  an  artistic 
street  instrument-shelter  designed  to  give  the  popu- 
lace of  large  cities  easy  access  to  weather  informa- 
tion. This  structure  was  of  enameled  white  cast- 
iron  with  four  plate-glass  sides  permitting  views  of 
meteorological  instruments,  weather  bulletins, 
charts,  etc.  It  was  explained  by  the  Washington 
officials  that  should  the  preliminary  tryout  prove 
satisfactory  it  was  the  intention  to  supply  the 
larger  cities  of  the  country  with  such  structures. 
This  street  instrument-shelter  was  called  a  "kiosk." 
Kiosk  is  a  Turkish  word  meaning  a  pavilion,  and 
is  sometimes  spelled  "kiosque."  It  is  pronounced 
with  the  accent  on  the  last  syllable  and  the  "i" 
short,  as  in  "it."  The  visiting  Californian  was 
impressed  with  the  utility  and  beauty  of  the  kiosk, 
and  thanks  to  the  interest  of  the  Chief  of  the 
Weather  Bureau  it  was  promised  that  San  Diego 
would  be  one  of  the  first  cities  out  of  Washington 
to  be  equipped  with  such  a  structure.  The  archi- 
tect of  the  plaza  fountain  (which  was  then  unthought 
of)  proffered  his  services  to  the  government,  and  the 
park  commissioners  proceeded  to  lay  out  the  plaza 
in  harmony  with  the  lines  of  the  kiosk  so  as  to  give  a 
fitting  setting.  The  city  authorities  desired  to  have 

(97) 


98       Climate  and  Weather  oj  San  Diego 

the  kiosk  in  the  center  of  the  plaza,  but  it  was 
pointed  out  to  them  that  such  a  location  should  be 
reserved  for  a  fountain.  In  the  spring  of  1909,  the 
kiosk  was  accepted  by  a  city  ordinance  from  the 
United  States  by  the  park  commission,  and  on  July 
8  the  recording  instruments  were  started.  While 
the  plaza  was  being  laid  out  Louis  J.  Wilde  saun- 
tered along  one  day,  and  when  it  was  explained  to 
him  that  the  center  of  the  plot  was  left  vacant  for 
an  electric  fountain  he  exclaimed:  "Go  ahead  with 
the  fountain— let  it  be  the  finest  of  its  kind."  The 
plaza  fountain  was  the  result,  and  it  is  the  admira- 
tion of  citizens  and  visitors  alike.  Thus  the  kiosk 
was  father  to  the  fountain. 

THE    KIOSK    SHOWS    THE    WEATHER    CONDITIONS    ON 
THE  STREET-LEVEL 

The  kiosk  is  a  well- ventilated  structure,  designed 
to  show  accurate  temperature,  humidity,  rainfall, 
and  barometric  conditions,  and  to  display  weather 
bulletins,  charts,  etc.  The  instruments  are  so 
arranged  as  to  be  in  easy  view  of  the  passerby  and 
yet  retain  their  proper  exposure.  This  is  accom- 
plished by  having  special  thermometers  made  with 
bulbs  projecting  12  inches  to  the  center  of  the  open 
air-space.  In  addition  to  a  thermometer  which 
continuously  records  the  temperature  for  a  period  of 
two  weeks,  there  are  two  mercurial  thermometers 
showing  extremes  of  temperature,  etc.  A  hair- 
hygrometer  shows  the  amount  of  moisture  in  the 
air  in  percentage  of  saturation,  and  the  barometer 
the  air-pressure.  Perhaps  the  most  ingenious  of  all 
the  instruments  is  the  rain-gage  which  admits  the 


ioo     Climate  and  Weather  oj  San  Diego 

rain  at  the  top  of  the  kiosk.  When  rain  enters  the 
receiver,  the  water  is  conveyed  to  a  double  compart- 
ment bucket,  each  compartment  holding  exactly 
o.o  i  of  an  inch.  When  one  of  the  compartments 
fills  it  is  overbalanced  and  in  tipping  actuates  a 
hand  which  marks  off  the  amount  on  a  dial.  A 
smaller  hand  shows  the  rainfall  in  inches.  In  the 
course  of  a  day  hundreds  of  persons  stop  in  front  of 
the  kiosk  and  note  the  weather  conditions.  It  is 
a  matter  of  considerable  satisfaction  to  the  people 
that  they  are  able  to  see  the  weather  records  in 
their  making.  The  records  are  at  the  level  of  the 
"man  on  the  street"  a  few  feet  above  the  sidewalk, 
exposed  to  summer  sun,  reflected  heat  of  surround- 
ing buildings,  and  the  cold  of  settling  air.  The  sole 
purpose  of  the  kiosk  thus  is  seen  to  be  for  the  accom- 
modation of  the  public.  For  official  use  or  climato- 
logical  purposes,  forecasting,  etc.,  it  is  necessary 
to  have  standardized  weather  records  free  from  all 
local  influences.  To  be  compared  with  other  stations 
of  the  Weather  Bureau  the  official  thermometers 
are  exposed  at  an  average  of  ioo  feet  elevation. 
This  explains  why  Weather  Bureau  thermometers 
are  always  located  in  the  free  air.  During  periods 
of  pronounced  air-drainage,  a  difference  in  tempera- 
ture of  as  many  as  ten  degrees  has  been  observed 
between  the  street  and  top  of  office  buildings. 
While  this  may  appear  to  be  a  considerable  varia- 
tion within  a  few  hundred  feet,  yet  there  is  prob- 
ably twice  this  difference  in  temperature  in  various 
parts  of  the  city.  For  example,  at  the  bottoms  of 
some  of  the  canons  in  San  Diego  County  frost  occurs 
twenty  or  thirty  nights  in  the  year.  It  will  thus  be 
seen  that  temperature  is  an  extremely  variable  quan- 


Weather  Kiosk  in  the  Plaza  101 

tity,  and  that  the  uses  to  which  observations  are  to 
be  put  determine  their  significance,  whether  it  is  to 
collect  climatic  records  for  standardizing  compari- 
son, for  the  convenience  of  pedestrians,  or  for  crops. 
By  experiment  it  is  possible  to  determine  the  aver- 
age difference  between  surroundings  and  so  secure 
what  is  termed  a  constant.  For  a  series  of  observa- 
tions extending  over  two  years,  the  kiosk  constant  is 
about  6  degrees;  that  is,  the  kiosk  shows  the  tem- 
perature averaging  3  degrees  higher  and  3  degrees 
lower  than  the  official  readings.  During  periods  of 
unusual  heat  or  cold,  these  variations  have  been 
doubled.  On  days  of  good  ventilation,  that  is,  when 
a  moderate  breeze  is  blowing,  there  is  little  differ- 
ence between  the  street-level  and  the  tops  of 
buildings. 

In  addition  to  its  function  as  an  instrument 
shelter  the  kiosk  displays  in  the  other  three  windows 
weather  bulletins,  charts,  etc.  The  western  window  is 
devoted  to  the  marine  meteorological  work  of  the 
local  station;  the  south  window  displays  cloud 
charts  and  illustrations;  and  the  east  window  con- 
tains a  copy  of  all  the  publications  of  the  local 
Weather  Office.  In  addition  to  the  seasonal  weather 
data,  the  monthly  summaries,  the  daily  weather 
map,  and  the  printed  bulletins,  a  card  index  is 
maintained  showing  daily  comparative  weather 
conditions  in  San  Diego  for  each  day  of  the  past 
forty  years. 


CHAPTER  XXV 
WEATHER  EXHIBITS  AT  WORLD'S  FAIRS* 

IT  is  difficult  to  advertise  a  climate  properly,  for 
statistical  tables,  columns  of  figures  and  weather 
charts  may  be  ever  so  carefully  compiled  and 
attractively  labeled,  but  the  general  public  balks 
at  tables  and  charts.  The  Board  of  Supervisors  of 
the  county  of  San  Diego,  CaL,  provided  the  neces- 
sary funds  to  prepare  an  attractive  and  practical 
method  of  showing  features  of  the  climate  of  San 
Diego  at  the  Alaska- Yukon-Pacific  Exposition  at 
Seattle,  Washington. 

The  San  Diego  climatic  exhibit  consists  of  three 
pieces  of  apparatus.  To  show  the  cool  summers  and 
the  warm  winters  of  San  Diego  an  electric-flasher- 
board  has  been  designed.  This  consists  of  a  sign  7 
feet  high  and  8  feet  long,  having  vertical  lines  and 
horizontal  divisions  showing  the  months  of  the 
year  and  temperatures  from  30  to  90  degrees. 
A  row  of  red  electric  lights  outlines  the  maximum 
temperature  for  every  month  of  the  year,  and  a  row 
of  blue  electric  lights  the  minimum  temperature  for 
a  corresponding  period.  Beginning  with  January, 
the  red  lights  burn  consecutively,  two  lights  for 
each  month,  until  the  whole  year's  monthly  maximum 
temperatures  are  displayed.  The  illuminated  trace 
requires  about  ten  seconds  to  traverse  the  twelve 
months.  These  lights  then  disappear,  and  a  line  of 
blue  lights  is  begun  on  the  minimum  portion  of  the 
board.  When  the  line  of  blue  lights  is  complete, 

*MonthIy  Weather  Review,  Vol.  XXXVII,  pp.  176, 177. 

(102) 


104     Climate  and  Weather  oj  San  Diego 

It  would  seem  practicable  to  apply  some  of  these 
methods  of  attracting  attention  to  more  serious 
purposes  than  advertising.  This  would  appear  to 
be  especially  true  of  the  illuminated  and  revolving 
globe.  The  boundaries  of  the  countries  of  the 
world,  the  seas,  the  islands,  and  their  designations 
are  painted  on  the  inside  of  the  globe.  Such  a  method 
allows  complete  isothermal  and  other  lines,  as  well 
as  the  distribution  of  winds  and  rainfall,  to  be  drawn 
in  water -colors  on  the  outside  of  the  glass.  Such 
drawings  could  be  easily  erased  or  changed. 

That  the  general  public  is  interested  and  studies 
such  a  climatic  display  was  shown  by  the  results  of 
the  preliminary  display  in  one  of  the  prominent 
store  windows  before  shipment  to  Seattle.  Several 
thousand  people  saw  this  exhibit  during  the  three 
days  it  was  shown  in  San  Diego. 

NOTE. — This  exhibit  was  awarded  a  gold  medal  at  the 
Seattle  World's  Fair.  Although  these  pieces  of  apparatus 
were  designed  primarily  for  this  fair,  the  exhibit  nas  con- 
tinued ever  since,  being  on  display  at  all  of  the  large 
expositions  and  fairs  throughout  the  United  States  for  the 
past  three  years.  At  present  this  exhibit  is  being  shown 
at  the  Los  Angeles  Chamber  of  Commerce,  where  it  has 
been  in  operation  during  the  intervals  when  no  fairs  or 
expositions  were  in  progress. 


CHAPTER  XXVI 
THE  WEATHER  BUREAU  AND  THE  PUBLIC 

A  FEW  years  ago  a  member  of  the  French 
Academy  of  Science  called  at  the  San  Diego 
Weather  Bureau  office,  and  having  been 
shown  the  meteorological  apparatus  and  informed 
as  to  the  application  of  the  data  to  the  everyday 
needs  of  commerce  and  agriculture,  exclaimed, 
"You  Americans  are  a  wonderful  people.  You  not 
only  equal  the  French  in  the  use  of  delicate  instru- 
ments from  which  theories  are  evolved,  but  you 
excel  us  in  making  the  results  worth  dollars  and 
cents."  And  had  this  French  scientist  visited  some 
of  the  Weather  Bureau  offices  in  the  flood  districts, 
or  the  cautionary  signal  stations  on  the  Great  Lakes, 
the  Gulf  of  Mexico,  or  the  Atlantic  coast,  he  could 
have  added  human  life  to  the  pecuniary  saving. 
An  article  in  the  Century  Magazine  a  few  years 
ago  stated  that  the  Weather  Bureau  costs  the  United 
States  a  million  and  a  half  dollars  a  year,  but  that 
a  conservative  insurance  company  figured  that  on  an 
average  the  people  of  the  United  States  saved  annu- 
ally $30,000,000  because  of  their  weather  service, 
and  this  in  addition  to  thousands  of  lives. 

THE  CURVE  OF  COMFORT 

The  perfect  adjustment  of  climate  and  health 
might  be  called  the  curve  of  comfort.  It  finds  full 
expression  in  San  Diego,  and  for  that  reason  it  is  not 
strange  that  some  people  think  the  work  of  the 

(105) 


io6     Climate  and  Weather  of  San  Diego 

weather  man  is  over  when  he  hangs  out  his  little 
card:  "Fair  tonight  and  Sunday." 

It  is  believed  that  San  Diego  offers  innumerable 
opportunities  to  show  the  ability  of  the  Weather 
Bureau  employes  in  perceiving  and  utilizing  the 
service  to  the  good  of  the  community.  Some  of  the 
practical  uses  of  the  Weather  Bureau  to  the  every- 
day walks  of  life  may  be  found  in  the  following 
quotation  from  the  act  of  Congress  of  1890,  which 
summarizes  the  general  functions  of  the  Weather 
Bureau: 

The  Weather  Bureau  shall  have  charge  oj  forecasting 
the  weather;  the  issue  of  storm  warnings,  the  display  of 
weather  and  flood  signals  for  the  benefit  of  agriculture, 
commerce  and  navigation;  the  gaging  and  reporting  of 
rivers;  the  maintenance  and  operation  ofseacoast  telegraph 
lines  and  the  collection  and  transmission  of  marine  intel- 
ligence for  the  benefit  of  commerce  and  navigation;  the 
reporting  of  temperature  and  rainfall  conditions  for  the 
cotton  interests;  the  display  of  frost,  cold  wave,  and  other 
signals;  the  distribution  of  meteorological  information 
in  the  interest  of  agriculture  and  commerce,  and  the  taking 
of  such  meteorological  observations  as  may  be  necessary 
to  establish  and  record  the  climatic  conditions  of  the 
United  States  or  are  essential  for  the  \proper  execution  of 
the  foregoing  duties. 

Among  the  ways  the  San  Diego  office  serves  the 
public  is  the  making  and  disseminating  of  weather, 
wind  and  temperature  forecasts,  issuance  and  dis- 
play of  storm  warnings,  and  frost  warnings;  printing 
and  distributing  daily,  monthly  and  annual  bulletins, 
furnishing  marine  intelligence,  the  compilation  of 
meteorological  data;  popularizing  meteorology;  sup- 
plying data  to  physicians  and  engineers;  testing 


Weather  Bureau  and  the  Public       107 

meteorological  instruments  for  local  use,   and  in 
producing  the  records  in  courts  of  justice. 

LOCAL  FORECASTS  ARE  MADE  AT  8  O*  CLOCK 

The  San  Diego  Weather  Bureau  office  receives 
every  morning  and  evening,  including  Sundays  and 
holidays,  telegraphic  weather  reports  from  one 
hundred  cities  in  the  United  States  and  Canada. 
These  messages  are  entered  on  a  large  outline  map 
of  the  United  States,  and  after  the  wind  direction, 
weather  and  precipitation  are  entered,  lines  are 
drawn  connecting  the  stations  with  equal  barometer 
and  thermometer  readings  and  the  forecast  for  the 
ensuing  thirty-six  hours  is  made.  The  daily  weather 
forecast  is  made  from  the  morning  report.  Messages 
are  received  as  early  as  seven  o'clock,  and  such  is 
the  celerity  made  possible  by  the  system  used  that 
with  a  force  of  only  three  employes  the  forecasts  are 
distributed  by  telephone  and  telegraph,  and  type- 
printed  bulletins,  forecast  cards  and  weather  maps 
are  mailed  and  posted  before  ten  o'clock.  In  excep- 
tional instances  the  published  reports  are  on  the 
streets  within  an  hour  after  the  last  telegraphic 
report  has  been  received.  The  forecasts  are  more 
widely  distributed  by  the  daily  newspapers  than  by 
any  other  method.  Next  in  value  comes  the  display 
of  the  weather  map  in  important  localities  about 
town.  As  the  map  is  limited  to  an  edition  of  125 
copies,  it  is  a  rule  of  the  office  that  it  must  be  posted 
so  that  not  less  than  twenty-five  people  see  it.  In 
addition,  the  office  printing  press  turns  out  several 
hundred  bulletins  and  forecast  cards  which  are 
mailed  regularly  to  interested  persons.  The  quickest 


io8     Climate  and  Weather  of  San  Diego 

method  of  disseminating  the  weather  forecast  is 
by  telephone.  Any  person  having  access  to  a  tele- 
phone may  obtain  the  weather  forecast  by  requesting 
it  of  "information,"  to  whom  it  is  given  at  nine 
o'clock  every  day.  Special  forecasts  may  be  obtained 
any  time  at  the  local  office.  During  threatening 
weather  the  four  telephones  in  the  office  are  kept 
busy  answering  calls.  On  one  threatening  morning 
the  calls  were  so  frequent  that  a  tally  was  kept, 
showing  that  between  the  hours  of  nine  and  twelve 
179  inquiries  had  been  answered.  Telephone  inqui- 
ries are  never  discouraged;  on  the  contrary,  the  public 
is  invited  to  call  up  the  Weather  Bureau  office  at 
any  time  for  any  weather  information  they  may 
wish. 

HOW  THE  FORECASTS  ARE  USED 

The  utilization  of  the  forecasts  by  the  public 
covers  a  wide  range.  A  few  of  the  uses  are  as  fol- 
lows: Protecting  the  raisin  crop  when  the  grapes 
are  drying  on  the  ground  in  the  autumn,  the  cutting 
of  hay  so  as  to  save  loss  by  showers,  and  also  pro- 
tection of  cattle  from  sudden  snowstorms  in  the 
mountain  meadows  in  the  autumn  and  winter.  The 
irrigation  of  citrus  orchards  is  governed  by  the  fore- 
casts, for  aside  from  waste  of  water,  considerable 
damage  results  if  rain  follows  a  generous  irrigation. 
The  stages  and  automobile  parties  rely  on  the  reports 
of  the  bureau  as  to  the  condition  of  roads,  etc.,  in 
the  back  country.  Other  occupations  affected  are 
building  operations  throughout  the  year,  and  the 
protection  of  perishable  goods  on  open  wharves  and 
docks.  Special  temperature  forecasts  are  used  by 


Weather  Bureau  and  the  Public        109 

ice  and  cold -storage  companies.  Shipments  of 
lemons  are  governed  largely  by  the  special  shippers' 
forecasts  of  probable  temperature  conditions  on 
interior  railroad  points.  Frost  warnings  have  been 
successfully  used  when  smudging  and  heating  the 
orange  groves  is  necessary.  Florists  growing  tropi- 
cal flowers  in  the  open  are  also  warned  of  dangerous 
temperatures.  Wind  forecasts  are  utilized  by  the 
fishing  fleet  and  small  craft  in  the  harbor  and  by 
tourists  in  making  excursions  to  neighboring  islands. 
Yachting  and  racing  boats  use  wind  forecasts  in 
preparing  for  special  events. 

Signals  are  displayed  on  the  Point  Loma  wireless 
masts,  on  the  top  of  the  Spreckels  Brothers'  coal 
bunkers,  and  on  the  boat-house  at  Coronado  beach. 
Shippers  claim  that  since  the  establishment  of  this 
station  San  Diego  has  never  experienced  high  winds 
without  storm  flags  having  been  flying  for  several 
hours.  Although  more  than  half  of  the  time  the 
signals  have  been  displayed  no  winds  of  conse- 
quence have  occurred  locally,  the  signals  are  some- 
times hoisted  for  the  use  of  shipmasters  sailing  to 
other  ports. 

WIRELESS  WEATHER  WARNINGS 

The  marine  interests  in  San  Diego  claim  that  the 
Weather  Bureau  is  of  no  little  value  to  them  in 
addition  to  the  usual  storm  signal  service.  Every 
deep-water  vessel  entering  the  port  of  San  Diego 
is  supplied  on  arrival  with  weather  and  wind  charts, 
and  on  their  departure  with  copies  of  the  daily 
weather  map  and  ocean  meteorological  charts  cover- 
ing their  outward  course.  Through  the  splendid 


no     Climate  and  Weather  of  San  Diego 

cooperation  of  the  wireless  operators  of  the  United 
States  navy  this  service  has  been  extended  to  include 
ships  within  the  wireless  radius  of  the  Point  Loma 
station.  Not  long  ago  a  foreign  vessel,  over  a  hun- 
dred miles  at  sea,  asked  for  weather  conditions 
over  the  proposed  course.  A  forecast  map  was 
hastily  constructed  by  the  aid  of  their  own  and 
coast  observations,  and  a  forecast  issued  to  them  in  a 
few  minutes.  When  the  naval  fleet  is  in  southern 
waters,  this  office  keeps  the  admiral  informed 
daily  by  wireless  of  existing  and  probable  weather 
conditions. 

THE     WEATHER     MAN*S     WORK     BEGINS     EARLY 

The  work  of  the  local  Weather  Office  begins  at 
4.40  A.M.  when  the  first  observation  of  the  day  is 
made.  Shortly  after  this  hour  the  simultaneous 
observations  begin  coming  in  by  telegraph.  Obser- 
vations are  also  made  at  noon,  and  at  4.40  P.M. 
The  office  is  open  until  the  last  telegraphic  report 
is  received  and  the  evening  weather  map  is  com- 
pleted, which  is  usually  about  seven  o'clock. 

Some  indirect  instruction  in  meteorology  is  given, 
but  of  necessity  to  a  limited  extent.  It  has  been 
found  that  the  best  medium  of  popular  meteorologi- 
cal information  is  the  kiosk  in  the  plaza;  as  a  means 
of  popularizing  meteorology  it  has  no  equal.  Other 
instruction  includes  visits  at  the  local  Weather  Office 
from  the  physical  geography  classes  of  the  normal 
school  and  cadets  from  training  ships.  Explanatory 
wind  and  pressure  charts  and  data  are  furnished  to 
the  aviation  school  on  North  Island. 


CHAPTER  XXVII 

THE  CLIMATE  SUMMARIZED   IN  FIVE 
PARAGRAPHS 

T"7^0R  sixteen  years  the  writer  has  been  in  charge 
H  of  the  local  office  of  the  United  States  Weather 
Bureau  in  San  Diego,  and  the  intimate  ac- 
quaintance thus  formed  with  the  climate  emboldens 
him  to  summarize  the  cardinal  features  in  the  five 
following  paragraphs  treating  on  the  temperature, 
rainfall,  wind,  sunshine,  and  comparative  seasonal 
temperatures: 

Temperature. — Since  the  beginning  of  meteoro- 
logical records,  the  temperature  has  averaged  less 
than  one  hour  per  year  above  90°.  Highest  and 
lowest  temperatures  ever  recorded  are  101°  and 
32°.  The  thermometer  has  never  gone  below  32°, 
and  no  snow  has  ever  fallen,  although  the  records 
extend  back  to  1871. 

Rainfall. — The  annual  rainfall  averages  ten  inches. 
Back  from  the  coast,  the  rainfall  increases  to  over 
forty  inches.  It  is  in  this  well-watered  region  that 
the  magnificent  water-supply  of  San  Diego  is 
located. 

Wind. — The  sea  breeze  keeps  San  Diego  cool  in 
summer  and  warm  in  winter,  and  the  nearby  moun- 
tains and  desert  give  it  a  dry  marine  climate.  The 
wind  averages  five  miles  per  hour  throughout  the 
year. 

Sunshine. — The  sun  shines  in  San  Diego  on  an 
average  of  356  days  a  year.  The  photographic 
sunshine  recorder  shows  that  for  over  twenty  years 

(in) 


H2     Climate  and  Weather  of  San  Diego 

there  has  been  an  average  of  less  than  nine  days  a 
year  without  one  hour  or  more  of  sunshine. 

Comparative  Seasonal  Temperatures. — Tempera- 
tures are  usually  shown  on  a  globe  by  lines  which 
pass  through  regions  of  the  same  degree  of  heat  or 
cold.  Red  lines  of  60°  and  70°,  showing  the  summer 
temperatures  at  San  Diego,  also  enclose  Alaska 
and  Siberia.  Blue  lines  of  50°  and  60°,  showing  the 
winter  temperature  at  San  Diego,  enclose  Egypt 
and  Arabia.  Thus  San  Diego  may  be  said  to  have 
Alaskan  summers  and  Egyptian  winters, 

NOTE. — After  these  pages  were  printed  occurred 
the  great  California  freeze  on  January  sixth  and 
seventh,  nineteen  thirteen.  The  temperature  at 
San  Diego  was  lower  than  32°  for  twelve  hours, 
reaching  the  absolute  minimum  of  25°  at  six  A.  M., 
January  seventh. 


Climate  and  Weather  oj  San  Diego     113 

TABLE  XIV.— Comparative  Meteorological  Data  Since  1872 


MONTH 

TEMPERATURE 

PRECIPITATION 

High- 
est 

Year 

Day 

Low- 
est 

Year 

Day 

24-hr, 
maxi- 
mum 

Year 

Day 

January  

83 
85 
99 
96 
98 
94 
93 
93 
101 
96 
93 
82 

1904 
1889 
1879 
1910 
1896 
1877 
1911 
1909 
1883 
1901 
1904 
1874 

13 

12 
29 
23 
25 
10 
14 
30 
22 
21 

6 

32 
34 
36 
39 
45 
50 
54 
54 
50 
44 
38 
32 

1880 
1891 
1894 
1875 
1883 
1884 
1880 
1879 
1880 
1878 
1881 
1879 

31 
10 
5 
7 
2 
14 
4 
29 
29 
30 
18 
25 

2.49 
2.39 
2.40 
1.20 
1.45 
.25 
.83 
1.80 
.37 
1.82 
2.75 
2.52 

1882 
1901 
1906 
1886 
1884 
1899 
1902 
1873 
1890 
1883 
1879 
1873 

12 
8-9 
24-25 
11-12 
14-15 
1 
24-25 
12 
28-29 
27 
9 
4 

March... 

April 

May...::::::: 

July  

August  
September.    .  . 
October  
November.    .  . 
December.  .   .  . 

MONTH 

WIND 

RELATIVE 
HUMIDITY 

SUNSHINE 

Max. 
Vel. 

Dir. 

Year 

Day 

A.M. 

P.M. 

No.  of 
Hrs. 

Pos- 
sible 

Per- 
Cent 
Poss. 

37 
40 
43 
39 
33 
24 
30 
25 
28 
32 
33 
38 

SE 
SE 

SW 

NW 
SW 
NW 
NW 
W 

w 

1873 
1878 
1912 
1877 
1905 
1886 
1881 
1900 
1881 
1877 
1905 
1906 

is 

9 

*T 

11 
2 
3 

7 
29 
27 
31 

73 

78 
80 
82 
82 
85 
87 
86 
84 
80 
72 
68 

69 
68 
68 
68 
72 
72 
74 
73 
72 
73 
70 
67 

218 
211 
242 
270 
247 
253 
292 
297 
271 
256 
238 
233 

318 
320 
372 
390 
430 
428 
437 
414 
371 
352 
314 
311 

68 
67 
64 
69 
57 
60 
67 
71 
73 
73 
76 
74 

February.  .  . 

March 

April  .... 
May  
June 

July... 

August 

September  
October 

November  
December  

1 14     Climate  and  Weather  of  San  Diego 


TABLE  XV. — Meteorological  Summary  of  San  Diego, 
California,  for  1911 


MONTH 
1911 

TEMPERATURE,  in  Degrees  Fahr. 

e 

1 

Mean 

Mean 

ft 

%X 

Absolute 

§ 

• 

i 

j^ts1 

*& 
11 

1 

S 

! 

January  

56.2 
52.2 
58.0 
57.7 
59.3 
62.4 
66.2 
67.4 
66.2 
63.0 
61.7 
53.4 
60.3 

*2.2 
-2.4 
*1.8 
-0.5 
-1.5 
-1.4 
-0.7 
-1.3 
-0.7 
0 
*2.7 
-2.3 
-0.3 

63.5 
59.1 
63.8 
63.2 
64.3 
67.2 
71.1 
72.8 
72.3 
70.6 
70.5 
61.9 
66.7 

48.9 
45.4 
52.3 
52.2 
54.3 
57.5 
61.2 
62.1 
60.1 
55.4 
52.9 
45.0 
53.9 

3 

2 
2 
1 
1 
2 
2 
2 
2 
2 
3 
2 
2 

15 
14 
12 
11 
10 
10 
10 

11 

12 
15 
18 
17 
13 

26 
26 
23 
29 
22 
32 
30 
18 
19 
28 
33 
24 
26 

77 
70 
77 
79 
74 
91 
93 
84 
76 
84 
82 
78 

93 

** 

41 
34 
44 
44 
49 
53 
59 
58 
54 
50 
44 
36 
34 

36 
36 
33 
35 
25 
38 
34 
26 
22 
34 
38 
42 
42 

February 

March...  

April... 

May 

June  

July 

August  

September  
October  

November  

December 

Mean  

*Excess. 


**JuIy  14. 


t  February  16. 


^December. 


MONTH 
1911 

;  RAINFALL 

i* 

1/1  rt 

£* 

i* 

II 
I'" 

Total 
Mid- 
night 
to 
Mid- 
night 

Depar- 
ture 
from 
Normal 

Greatest  in 
34  hours 

Number  of  Days  With 

Sfi 

s| 

II 

11 

s« 

S3 

d 

1 

January  
February  
March 

1.59 
3.84 
.45 
.33 
.00 
.01 
.03 
.00 
.01 
.27 
.02 
.58 
5.13 

1.76 
3.08 
.47 
.32 
.01 
.00 
.09 
.00 
.09 
.01 
.00 
.81 
6.64 

3.35 
4.92 
.92 
.65 
.01 
.01 
.12 
.00 
.10 
.28 
.02 
1.39 
11.77 

*1.35 
*2.96 
-   .78 
-  .09 
-  .40 
-  .02 
*  .12 
.00 
*  .04 
-  .18 
-  .81 
-  .43 
*1.76 

2.17 
1.69 
.37 
.36 
.01 
.01 
.05 
.0 
.09 
.28 
.02 
.56 
2.17 

9-10 
27-28 
3 
1-2 
5 
20 
10 

"30 
26-27 
10 
20 
Jan.  9- 
10 

9 
11 
7 
5 
1 
1 
4 
0 
2 
2 
1 
8 
51 

8 
11 
5 
4 
0 
0 
2 
0 
1 
2 
0 
7 
40 

4 
5 
2 
1 
0 
0 
0 

o 

0 
0 
0 
3 
15 

1 

2 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
3 

April... 

May  

July  

August  

September.  .  . 
October  
November..  .  . 
December.  .  .  . 
Mean  

*Excess. 


Climate  and  Weather  of  San  Diego     1 15 

TABLE  XV — Meteorological  Summary  oj  San  Diego, 
California,  /or  IQII,  continued 


MONTH 
1911 

WEATHER 

Sun- 
shine 

% 

3  0 

Iv 

>  c5 
•<t75 

Number  of  Days 

Number  of  Days 

1 

II 

! 

I 

1 

I 

i. 

January  

54 
63 
56 
62 
67 
55 
57 
78 
76 
82 
79 
79 
67 

4.7 
4.0 
4.5 
3.7 
3.3 
4.6 
4.4 
2.0 
2.5 
1.9 
2.0 
2.2 
3.3 

15 
13 
14 
16 
20 
13 
15 
28 
25 
23 
22 
21 
225 

5 
8 
9 
10 
8 
11 
12 
3 
2 
8 
7 
8 
91 

11 

7 
8 
4 
3 
6 
4 
0 
3 
0 
1 
2 
49 

4 
1 
1 
0 
2 
1 
3 
3 
6 
5 
0 
0 
26 

0 
1 
0 
0 
0 
0 
0 
0 
0 
0 
0 

1 

2 

0 
1 

0 
0 
0 
0 
0 
0 
0 
0 

1 

6 

8 

0 
0 
0 
0 

0 
0 
3 
0 
0 
0 
0 
2 
5 

March  

April   .  .  . 

May 

June  

Julv 

August  

September  

October  

November  

December  

Mean  

MONTH 
1911 

WIND 

Air  and  Sea  Temperature 
in  Harbor  at  12  Noon 
Local  Time,  1910 

| 

i 
li 

«8 

2s 

II 
§£ 

B 

Maximum  Velocity 

Average 

Extremes 

S 

«§3 
SJ 

| 

1 

4 

58 
59 
61 
66 
64 
64 
70 
71 
71 
69 
64 
62 
64.8 

1 

Water 

I 

J 

54 
55 
67 
63 
67 
68 
71 
71 
70 
64 
61 
56 
54 

January 

3661 
4365 
4179 
4502 
4874 
4811 
4620 
4446 
4565 
3876 
3907 
4343 
52149 

NE 
E 

NW 
NW 
NW 

NW 
NW 
NW 
NW 
NW 
NE 
NE 
NW 

4.9 
6.5 
5.6 
6.3 
6.6 
6.7 
6.2 
6.0 
6.3 
5.2 
5.4 
5.8 
6.0 

21 
26 
26 
23 
21 
23 
26 
22 
23 
21 
19 
26 
26 

S 
W 
S 

NW 
NW 
NW 
NW 
NW 
NW 
NW 
NW 
W 

10 
25 
3 
6 
21 
5 
14 
15 
24 
2 
22 
17 
*25 

55 
56 
61 
66 
69 
69 
72 
72 
73 
67 
64 
58 
65.2 

56 
57 
63 
69 
70 
70 
72 
74 
75 
71 
66 
60 
75 

February  
March  
April 

May.... 

July  

August  
September  .  .    . 

October  

November  

December  

Mean.  .  . 

*Feb.  25. 
H 

INDEX 


Air-dra 


Agassiz  (A.)  climate  of  San  Diego, 

frainage,  46,  68,  100. 

—  saturated,  9,  12,  13. 
Alaskan- Yukon-Pacific  Exposition, 

102. 

Anemometer,  63,  92,  96. 
Anemograph,  92. 
Anemoscope,  63. 
Auroras,  62,  63. 
Aviation,  57. 

Barograph,  63,  93. 
Barometer,  aneroid,  17,  93. 

—  mercurial,  63,  03. 
Birds  and  storm  winds,  90. 
Breezes,  Land  and  Sea,  54,  55- 

—  valley,  59. 

Cabrillo     (J.     R.)     first     weather 

observer,  3,  80. 
Chanute  (O.)  local  winds,  57. 
Climate,  changes  in,  33. 

—  classification,  48,  51. 

—  coast  and  bay  region,  48,  50. 

—  cycles  in,  33. 

—  desert,  fi. 

—  equability,  41. 

—  mountain,  49. 

—  stability,  34. 

—  summarized,  in. 
Climatic  factors  in  building,  44. 
Clouds,  alto-stratus,  10. 

—  alto-cumulus,  10. 

—  alto-stratus,  10 

—  cirro-cumulus,  10. 

—  cirro-stratus,  10. 

—  cirrus,  10. 

—  classification,  8. 

—  cumulo-nimbus,  10. 

—  cumulo-stratus,  10. 

—  cumulus,  9,  ip. 

—  cumulus  "whirling,"  n. 
thunderstorms,  10. 

—  nimbus,  65,  "festooned,"  n. 

—  Point  Loma  crest  explained,  9. 

—  stratus,  p. 

—  "table  cloth,"  9, 

—  velo,  7,  9,  89-. 

—  best  weather  indicators,  89. 


Cloud  banners,  1 1 . 
Condensation  and  clouds,  8. 

—  fog  formation,  20. 

—  radiation,  20. 

—  concussion,  28. 
Coronae,  61. 

Curtiss  (G.)  aviation,  58. 
Curve  of  comfort,  105. 
Cuyamaca  Peak,  10,  n,  52. 

Dana  (R.  H.)  southeaster,  3. 
"Desert  winds,"  12,  16,  17,  18. 
Dust  storms,  16,  17- 

Exhibits  at  World's  Fairs,  102. 

Farallone  Islands,  41. 
Fisher  (G.  P.)  myths,  78. 
Fog  aids  vegetation,  22,  23. 

—  cause,  19. 

—  data,  115. 

—  frequency  by  hours,  22. 
by  months,  21. 

—  "high"  (see  velo  cloud),  9. 
Forecasts,  how  made,  83,  107. 

—  utility,  1 08,  109. 

Franklin  (B  )  ocean  temperatures, 

80. 
Frost,  67. 

—  absence  of  killing,  45,  68. 

—  data,  115. 

—  warnings,  109. 

Gemenius  opposes  stellar  influence, 

79. 
Gibbon  (Lt.)    invents   anemograph 

Glacial*  period,  33. 

Greely    (A.  W.)     defines    climate, 

3,  4,  52. 
Gulf  Stream,  70. 

Hail,  data,  115. 
Halos,  lunar,  or. 

—  solar,  61. 

Herschel  (W.)  lunar  control,  77. 
Hellman  (G.)  weather  proverbs,  79. 
Humidity,  absolute,  15. 

—  relative,  12-15,  H3- 
how  measured,  94. 


(116) 


Index 


117 


Humidity,  relative,  relation  to  wind, 

13,  14- 

--  mean,  13. 
Humphreys    (W.    J.)    oceanic    in- 

fluence, XI,  69. 
Hydroaeroplane,  58. 
Hygrometer,  hair,  98. 
—  marine,  63. 
Hygrograph,  63,  94. 

Instruments,  meteorological,  92. 
Japanese  Current,  26,  70. 
Kiosk,  97,  no. 
Langley  (S.  P.)  aviation,  57- 

McAdie  (A.  G.)  California  rainfall, 
I,  53. 


XIII,  53. 
Manney    (H.   N.)    naval    wireless, 

81. 
Maury  (M.  F.)  marine  meteorology, 

Maps,  weather,  making,  83-86. 

—  used  in  forecasting,  85. 
Marine  meteorology,  80,  81,  82,  109, 

no. 

Medical  Corps,  U.  S.  A.,  work  of,i. 
Meteorological  Instruments,  63. 

—  myths,  75. 
Metrograph,  63,  96. 
Mirage,  60. 

Moon  does  not  affect  the  weather, 

MoorZ'ffi.  L.)  V.  VIII,  102. 
Mountains  and  climate,  50. 

Ocean  currents  and  climate,  27. 
Ocean,  effect  on  frost  level,  68. 
--  on  temperatures,  41,  68. 

—  inter-relation  with  weather,  69. 

—  temperature  of,  80. 
Optical  phenomena,  60. 

Palomar  Mountain,  clouds  on,  10. 
Precipitation  (see  also  Rainfall). 

—  average  annual  in  California,  53 
Pressure,  atmospheric,  17- 

—  highs  (centers  of  action),  17,  73, 

84. 

—  in  thunderstorms,  64. 

—  lows  (centers  of  action)  25,  27, 

84. 

—  mapping  of,  84.  85. 
Proverbs,  weather,  90, 


Psychrometer,  whirled,  63,  94. 

—  sling,  63. 

Rain,  36,  37,  H3t  "4- 

—  cause,  26.^ 

—  comparative  annual,  51,  53. 

—  gages  for  measuring,  24,  63,  95, 

96,  100. 

—  manufacture   not   possible,    20. 
Rainfall,  average  number  days,  25, 

26. 

—  distribution,  24,  29. 

—  excessive  (at  Campo)  52. 

—  variation,  seasonal,  24,  29,  31, 

altitude,  49,  51. 

diurnal,  114. 

Rainbow,  90. 

Salton  Sea,  26. 

San  Diego  County  data,  49- 

Serra  (Fr.  J.)  founded  first  mission, 

Signal  Corps,  U.  S.  A.  4. 

Snow  unknown  in  San  Diego,  in. 

Soil,  16. 

Storm  warnings,  100. 

Storms,  circulation  in,  26,  84,  86. 

—  "equinoctial,"  27,  76. 

—  forecasting,  83. 

—  movement,  83. 

—  paths,  86. 
"Sonoras,"  10.  32. 
Sundogs,  n,  62. 
Sunshine  data,  113,  115. 

—  record,  43,  9<5,  "3- 

—  recorder,  electric,  95. 
photographic,  63. 

Telethermoscope,  electric,  63,  94 
Temperature,  annual,  34. 

—  bay  and  ocean,  115. 

—  extreme,  113,  114. 

—  effect  of  elevation,  52. 
of  latitude,  41- 

—  highest,  42. 

—  kiosk,  1 01. 

—  lowest,  42,  113. 

—  uniformity  of,  34,  41- 
Thermometers,  63,  93. 
Thermograph,  63,  94. 

—  kiosk,  99. 
Thunderstorms,  64. 

—  cloud  features  in,  10. 

—  data,  115. 

—  hourly  distribution,  65 


n8 


Index 


Thunderstorms,  daily  distribution, 

64. 
—  monthly  distribution,  115. 

Ubach  (Fr.  A.  D.)  prayers  for  rain, 
90. 

Ventilation,  46. 

Viscaino  (Don.  S.)  surveyed  harbor. 

Volcano  Springs,  data,  52. 

Warnings,  storm,  108. 

Waterspouts,  65,  66. 

Weather  Bureau,  functions,  106. 


Weather   data,   comparative,  113- 
115. 

—  map,  10,  71,  85,  107. 

—  observations,  history,  i,  3. 
__  location,  2. 

—  "signs,"  88-91. 

Wilde  (L.  J.)  fountain-kiosk,  98. 
Wind,  direction,  50,  54,  113-115. 

—  "norther,"  18, 

—  "Santa  Ana,"  17,  18. 

—  "southeaster,"  3. 

—  velocity,  51,  55,  57,  ,I3,  ,,5, 
Winds,  cause  of  54,  17,  54. 

—  moisture-bearing,  14. 

—  velocity  and  frequency,  50. 
Wright  (O.)  aviation,  57. 


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